Political parties in Wales have been paid almost £500,000 from public funds over the past two years for office space for their AMs and MPs.
The four main parties received at least £236,000 in 2007/8 and about £242,000 in 2008/9 in rental payments from Welsh assembly and parliamentary authorities.
BBC Wales research shows in some cases parties own the buildings where the offices are located.
In other cases, parties sub-let offices to AMs and MPs from landlords.
In some cases, the payments incorporate other costs (such as rates, utility, insurance and maintenance) as well as the actual rent, while in other constituencies these costs are claimed separately.
In addition, there are examples of political parties receiving payments from the public purse for providing other office facilities and support other than rent.
While none of these claims are against the existing rules, the Taxpayers' Alliance has described this as a "staggering amount of money", with the taxpayer "effectively funding political parties".
Many taxpayers will be surprised and deeply concerned that their money is being used to this end
Susie Squire, the Taxpayers' Alliance
With no evidence of a consistent approach towards an independent assessment of the market value of these rental arrangements, the level of rent paid for constituency offices across Wales varies significantly.
AMs and MPs often share office facilities at the same address - which accounts for around half of the office arrangements across Wales' 40 constituencies.
Despite the efficiency savings that could be made from such shared arrangements, the data provided from the expenses claims of MPs and AMs as well as local party accounts registered at the Electoral Commission, indicate that some local parties appear to be receiving a higher level of rent than may otherwise be paid for similar facilities in the surrounding area.
The four main political parties in Wales have claimed neary £500,000 in rent sometimes for buildings they themselves own
BBC Wales requested clarification from all four political parties regarding their financial arrangements in a number of constituencies across Wales.
Susie Squire, campaigns manager for the Taxpayers' Alliance, said: "It's a staggering amount of money.
"Many taxpayers will be surprised and deeply concerned that their money is being used to this end, and it's deeply regrettable that MPs, AMs, any elected official, hasn't been more open about what is effectively taxpayers' money funding political parties.
"They haven't been open about it, for how long they've been doing it, and how much money the political parties have received as a result of these arrangements."
Sir Alistair Graham, former chair of the Committee on Standards in Public Life, argued that the question of the true market value of the rent charged to the taxpayer is crucial.
"If the charges are being levied for the accommodation well above the market rate - then it's a diversion of public funds to political parties," he said.
"If that's being done it should be an accountable transparent arrangement which should be in the public arena - people should know that this is a conscious contribution to party funding rather than something done in a back door way - that's the key issue."
Although some of the published details for the parties across Wales are incomplete, the available data suggests that in the two years between April 2007 and March 2009, Labour party constituencies received rental payments of approximately £172,000, Plaid Cymru branches received around £108,000, Welsh Conservative Associations were paid in the region of £107,000, and the Liberal Democrats received just over £90,000.
Next week, an Independent Review Panel chaired by Sir Roger Jones is expected to publish a report that will lead to changes in the rules for financial support provided for assembly members, encompassing pay, allowances and resources - including whether or not the Welsh taxpayer should pay political parties for providing constituency or regional offices to their elected politicians.
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