I can't say that I've experienced anything similar recently, but it's possible that there may be a glitch on the site which is affecting some users and not others. To check whether or not this is indeed the case log out of eBay UK and log into one of eBay's overseas sites. Whenever I've encountered problems with making payment on eBay that were due to site glitches I've found that by logging out of eBay UK and logging onto the USA version of the site I've been able to make payment for the item that I was trying to buy.
If you do decide to give this a try the web address for the USA version of the site is www.ebay.com. The prices will all show up in US Dollars as opposed to Pounds Sterling, but at least the text will still show up in English so there shouldn't be any problems with regards to a language barrier. If you can make payment using that workaround option then it will do away with the problem of the seller losing his/her patience with you and opening an Unpaid Item Dispute in the mistaken belief that you've got no intention of paying for the item.
