I have just gotten off the phone with UK Deed Poll Service (0800 4488484) and they said do not worry, you have six months to change it, fly on your existing passport and tickets with your previous name and change it when you get back from any holidays or trips. They don't pass on the information to anyone so no-one else knows your name has been changed until you notify anyone like the passport office or the DVLA etc. So you won't be passing through customs, have your passport scanned and asked why you don't exist!
