I was hoping Splinter Cell Conviction would have been cheaper, but thanks to HUKD someone posted a link to get it even cheaper, though it is for the direct Uplay version, rather than Steam (which then requires Uplay).
Splinter Cell Blacklist £5.99
cd key came within 5 mins, activated straight on Uplay, where I then bought both DLC packs (75% off - £1.97) to effectively get the Digital Deluxe edition for less than 8 quid :)
Also picked up The Bureau XCOM Declassified for £3.99. That was a straight forward Steam key. Can't say I'm expecting it to be of the calibre of XCOM Enemy Unknown, but for 4 quid I'll take a gamble on it.