MPs and peers are facing questions about hundreds of thousands of pounds a year in expenses for trips to meet foreign counterparts.
Politicians have run up big bills attending little-noted Council of Europe sessions in locations such as New York, Helsinki, Vienna, Madrid, Paris and Brussels.
Delegations to parliamentary assemblies for Nato and the Organisation for Security and Co-operation in Europe (OSCE) have also spent significant sums.
In one case, Liberal Democrat Mark Oaten is recorded as making a £2,000 taxpayer-funded trip to Athens for a meeting of a body that was being abolished – despite no longer being an MP.
Details of the expenditure have come to light following a freedom of information request.
The Parliamentary Assembly of the Council of Europe (Pace) meets four times a year to “debate current social problems and aspects of international politics”. There are also 10 committees to prepare for the sessions.
The British delegation is appointed by the Prime Minister and reflects the composition of Parliament. There are 18 full members across both houses and another 18 “alternates” who can fill in when required.
According to material disclosed by the Commons, the delegation’s travel and subsistence costs came to £298,000 in 2013-14.
The bill for the first nine months of 2014-15 was more than £220,000.
The information reveals:
l Mike Hancock represented the UK at a three-day meeting of the political affairs committee in New York City in November last year – two months after he quit the Liberal Democrats over an “inappropriate” relationship with a vulnerable constituent.
His flights and travel came to £4,356, and hotel and subsistence £1,096.
l Former deputy prime minister Lord Prescott went to Monaco for a one-day meeting about sustainable development in March 2011, with travel £750 and subsistence £574.
l Tories Christopher Chope and Bob Neill had travel costs of £832 and £838 respectively for a two-day legal affairs committee meeting in Madrid last October.
Mr Neill said he had to “take what flights were available” at short notice due to business at Westminster, but they had been “within cost parameters” and booked by the Commons travel office.
He added that the meeting was “important” because there was a discussion of European Court of Human Rights (ECHR) decisions.
l Hereditary peer the Earl of Dundee attended a one-day social affairs committee meeting in Paris in December last year, which cost £363 for travel and £320 for hotel and subsistence.
l Jim Hood, Labour’s former MP for Lanark and Hamilton East, is listed as incurring a £1,400 travel bill to get to a session of the migration, refugees and displaced persons committee in Paris in June 2013. There was also a £305 hotel and subsistence bill for the one-day event.
The following May, £1,190 was spent getting him to Athens for a meeting of the political affairs committee – and another £421 on subsistence.
l Quarterly plenary sessions in Strasbourg last for five days and are typically attended by around 25 MPs and peers. The expenses bill for the British taxpayer from the event in October 2013 was around £48,000. Information has also been released about the costs of delegations to the parliamentary assemblies for Nato and the OSCE.
In 2013-14, the 18-member UK delegation incurred £235,666 in expenses.
The TaxPayers’ Alliance said: “Many of the figures suggest MPs were enjoying first or business-class travel on the taxpayers’ tab.”