http://ukhousing.wikia.com/wiki/Tower_block
Ok, so ~6,535 were built in the post war period. Building slowed dramatically after this period, and we've gotten to a point where we're seeing demolition of tower blocks, rather than building new ones.
Let's guess high, and say 10,000 tower blocks. This is a ridiculously high figure. The general election cost us somewhere around £150,000,000. This would at the worst case, be £15,000 per tower block.
But 'only' 4,000 tower blocks in the UK don't have sprinkler systems installed.
http://www.dailymail.co.uk/news/article-4602672/May-adviser-failied-act-warnings-tower-fire.html
So that's actually £37.5k for each block.
This is still significantly lower, however, than the cost of installing sprinkler systems in a tower block. It's pretty difficult to find many numbers on this, but there's a few estimates here: