The Houses of Parliament - an iconic London site that attracts visitors from all over the world.

Tourism is now worth 22.1 billion pounds (32 billion US dollars) annually to the UK, according to Visit Britain, Britain's national tourism agency.

Visit Britain also said that last year there were 36.1 million tourist visits, with 67 percent from the European Union.

On 23 June, the UK will vote in a referendum whether to stay in or out of the EU and many in the tourist industry are concerned that a possible leave vote will jeopardise the European holiday market.

One of those is Kyle Haughton, managing director of City Cruises.

His cruise ships carry 6 million passengers a year - in the height of summer 60 percent are from abroad, the majority from the EU.

Of the 240 staff that he employs, 50 percent are from outside the UK, mostly from the EU.

"Any change or decline in passengers coming into the country is going to affect our business quite lot and there are reports that people in Germany, Italy and France are less likely to come to the UK if we leave the EU than if we stay."

His fears are backed up by UK Inbound, which represents 360 tourist businesses.

Deidre Wells, chief executive of UKinbound has called leaving the EU "economic suicide."

"Why would you remove yourself from a market that provides two thirds of our business for our members," she said.

Tourists had mixed views about a UK "brexit".

Marco Ghiribelli, an Italian tourist, said he thought the UK would be economically better outside.

"It's not economically convenient for the UK to stay in the EU. Brexit makes sense economically as the UK economy is stronger than most of the EU countries."

Others such as Babette Pascalev, a tourist from Germany, said: "I think it is hard now because the idea is to get Europe together not apart."

But others say a Brexit would not make any difference to the tourism business.

They say nothing will change.

Alexander Goransson, travel analyst at Euromonitor International believes the expected drop in sterling following a brexit vote would attract tourists due to an increased spending power.

"In the short term I would expect to see a depreciation of the pound which will have both a positive and negative impact on tourism. UK tourists would be less likely to travel abroad and stay at home, whereas on the other hand the UK would actually become a more attractive destination for inbound tourists as prices would be relatively cheaper."

But most people in the tourist industry are hoping for a remain vote on June 23.

The Houses of Parliament - an iconic London site that attracts visitors from all over the world.

Tourism is now worth 22.1 billion pounds (32 billion US dollars) annually to the UK, according to Visit Britain, Britain's national tourism agency.

Visit Britain also said that last year there were 36.1 million tourist visits, with 67 percent from the European Union.

On 23 June, the UK will vote in a referendum whether to stay in or out of the EU and many in the tourist industry are concerned that a possible leave vote will jeopardise the European holiday market.

One of those is Kyle Haughton, managing director of City Cruises.

His cruise ships carry 6 million passengers a year - in the height of summer 60 percent are from abroad, the majority from the EU.

Of the 240 staff that he employs, 50 percent are from outside the UK, mostly from the EU.

"Any change or decline in passengers coming into the country is going to affect our business quite lot and there are reports that people in Germany, Italy and France are less likely to come to the UK if we leave the EU than if we stay."

His fears are backed up by UK Inbound, which represents 360 tourist businesses.

Deidre Wells, chief executive of UKinbound has called leaving the EU "economic suicide."

"Why would you remove yourself from a market that provides two thirds of our business for our members," she said.

Tourists had mixed views about a UK "brexit".

Marco Ghiribelli, an Italian tourist, said he thought the UK would be economically better outside.

"It's not economically convenient for the UK to stay in the EU. Brexit makes sense economically as the UK economy is stronger than most of the EU countries."

Others such as Babette Pascalev, a tourist from Germany, said: "I think it is hard now because the idea is to get Europe together not apart."

But others say a Brexit would not make any difference to the tourism business.

They say nothing will change.

Alexander Goransson, travel analyst at Euromonitor International believes the expected drop in sterling following a brexit vote would attract tourists due to an increased spending power.

"In the short term I would expect to see a depreciation of the pound which will have both a positive and negative impact on tourism. UK tourists would be less likely to travel abroad and stay at home, whereas on the other hand the UK would actually become a more attractive destination for inbound tourists as prices would be relatively cheaper."

But most people in the tourist industry are hoping for a remain vote on June 23.

London - 2 June 2016

1. Houses of Parliament seen from a river cruise boat

2. Woman taking picture of the Houses of Parliament

3. The London Eye seen from a river cruise boat

4. Part of the London Eye

5. Woman taking photo

6. People on board the river cruise boat

7. St Paul's Cathedral and other buildings

8. River cruise boat approaching Tower Bridge

9. Set up of Kyle Haughton, managing director of City Cruises

10. SOUNDBITE (English) Kyle Haughton, managing director of City Cruises:

"At City Cruises we carry 4 million passengers a year and over half of them come from overseas, the majority of which coming from EU countries, so any change or decline in passengers coming into the country is going to affect our business quite lot and there are reports that people in Germany, Italy and France are less likely to come to the UK if we leave the EU than if we stay."

London - 1 June 2016

11. Various of Deidre Wells, chief executive of UKinbound, at her desk

12. SOUNDBITE (English) Deidre Wells, chief executive of UKinbound:

"I've described it as economic suicide in the past. Why would you deliberately remove yourself from a market that provides two thirds of our business for our members."

London - 2 June 2016

13. People on board the river cruise boat with the Shard in the background

14. Set up of French tourist Kahina Berroua

15. SOUNDBITE (French) Kahina Berroua, French tourist:

"I will be sad. The UK has a lot of power in Europe so it won't be the same."

16. Various of tourists inside the river cruise boat

17. Set up of Marco Ghiribelli, Italian tourist

18. SOUNDBITE (Italian) Marco Ghiribelli, Italian tourist:

"It's not economically convenient for the UK to stay in the EU. Brexit makes sense economically as the UK economy is stronger than most of the EU countries."

19. SOUNDBITE (German) Babette Pascalev, tourist from Germany:

"I think it is hard now because the idea is to get Europe together not apart."

20. Houses of Parliament with open top tourist bus driving past

21. Union Jack flag on top of the Houses of Parliament

22. People on open top bus driving past the Houses of Parliament

23. People on bus

24. People on bus driving past flags

25. Various of Alexander Goransson, travel analyst at Euromonitor International, on laptop

26. SOUNDBITE Alexander Goransson, travel analyst at Euromonitor International:

"In the short term I would expect to see a depreciation of the pound which will have both a positive and negative impact on tourism. UK tourists would be less likely to travel abroad and stay at home, whereas on the other hand the UK would actually become a more attractive destination for inbound tourists as prices would be relatively cheaper."

27. People on open top bus

28. View of London black cabs and Union Jack flags