The 'regulation 2 metres' that you refer to only applies to permanet structures (i.e. a fence or a wall)!
Although there has been talk of amending the law to include hedges!
You do not need to cut your hedge. The only law, as far as I am aware, that could be used against you is 'Ancient lights'. Basically the other property owners would have to show that light which their property had enjoyed for 20 years or more was being denied them. Which, in this case, it clearly isn't as it's a new building!