This phone is still very rare in the UK and especially hard to get in Black at the moment. Mine should arrive today, but I thought as I have already been looking around I would just give others a heads up on where to get one of these with the best deal if they wanted.
One thing to make sure of 1st is that if in the UK you are getting the Euro version and NOT the Asian one. The difference is that the Euro One SV supports 3 LTE frequencies: LTE 800 / 1800 / 2600 (Europe) as opposed to just two for Asia: LTE 1800 / 2600 (Asia).
HTC One SV - Full phone specifications
I shall be checking the IMEI directly with HTC when mine arrives just to make sure.
These phones come in black, white, red and blue but white seems to be the one most available here and the white or blue one goes for about £260 on Amazon. If you want the black one and want to get it at a reasonable price here are some links. Stock seems to go up and down but the price is roughly about £280 or just a tad under. There is much more availability at the £330-350 mark but this seems excessive to be paying an extra £50-70 just for a different colour.
HTC One SV LTE SIM Free / Unlocked (Black) - HTC Smartphones - Smartphones - Mobile Phones | ValueBasket GB (only supply Asian version)
HTC One SV LTE Black Sim Free / Unlocked (only supply Asian version)
Mobile Phones MP3iPodMobiles - HTC One SV (Black) Android 4.0 SIM Free / Unlocked
Obviously i can't vouch for any of these companies but seem to be the cheapest place to get a black one.
Virgin mobile also have some good contract deals on these also i found. Happy shopping.
EDIT
My phone arrived and despite the assurances given by value basket (both via phone & email confirmation) that they would supply a European version intended for the UK market, I received the Asian model. There wasn't even a phone charger included! Now lets see how promptly they can supply the correct replacement.
It seems the only ones available in the UK and rest of Europe are the white and blue phones. Value basket are collecting and refunding for mine.
Currently then Amazon or Expansys seem the cheapest Eu versions available at £260.