It is getting ridiculously hard to get bitcoins in the U.K. International wires are to expensive, my bank doesn't support SEPA. I'm seriously thinking about converting ukash vouchers to cash u account, funding okpay with that. Then using that option at mtgox. There must be easier way.
Lloyd's answer using blockchain sounds like the best if you haven't already bought the UKash vouchers.
If you do have the UKash, then an alternative is to deposit UKash at VirWoX, then convert to SLL, then to BTC. I just tried it. It was quick and easy, but I worked out that I ended up paying ~£5 in transaction fees on an original UKash value of £20, so its not very efficient.
There are also restrictions on VirWoX that you can only convert whole GBPs and you must buy a minimum of 0.2 BTC. There is a 15% deposit fee on UKash, which with £10 vouchers leaves you with £8.50 - 50p of which cannot be used because of the whole GBP restriction. Depending on the exchange rate the £8 might not be tradable if it is worth less than 0.2 BTC. (You may have guessed that I experimented with a £10 UKash voucher then had to go and buy another one).