set up a € denominated bank account at your UK banking provider – Barclays e.g. can link a € a/c to your £ current account.
DO NOT tranfser the £ to that account through the bank!
Use transferwise.com to move the money by BACS from your £ a/c to your € a/c. Befor eyou do so, dro me an email and I have an introd code which should save you some fees.
transferwise fees are 0.5% and the rate is at the mid market price. So you pay v v little for the exchange. Your bank will say something daft like “no fees” but then transfer at a really crap spread on the mid market rate equivalent to nearly 5% off.
You will save something like £5k.
I did the same earlier this year, before I set up my french € a/c
I dont use my Barclays €, but having it was the best way of holding € in time for a transaction, but the french a/c is much more useful for day to day.