As Dzug has indicated, anyone who can reliably predict future exchange rates should be looking for a job in the City of London. (The people who do that successfully are the type of people who get half a million pounds bonuses,on top of a massive salary. Even they tend to get it wrong rather more often than they'd like to admit to).
The question of where (rather than when) to obtain euros comes up here frequently. Most people agree that the best way to get euros is to avoid bureaux de change facilities (especially those at airports and ferry terminals) and simply use a debit or credit card at overseas ATMs. Some banks make a charge for overseas cash withdrawal but, even allowing for the charge, you still get a better deal than changing your money in the UK. However, some banks make no charge for overseas cash withdrawals (with certain types of account). Many people open a Nationwide FlexAccount specifically for their holiday funds.
To return to your question, even if the exchange rate operates in favour of changing your money now, rather than later, you'll probably lose as much (or more) by changing your money here in the UK, rather than waiting until you're abroad. Open a suitable bank account (such as the Nationwide FlexAccount) for your holiday funds. If you happen to be taking a day trip abroad before July, it might be worth getting your holiday euros at an overseas ATM during that trip, but there probably won't be much difference if you wait until July. (i.e. it's probably more important to think about where you change your money, rather than when).
Chris