Might be me but I can't find any charge of £4.
Think I stick to PNB which basically offer the same exchange rate and charge £5 for a bank to bank transfer of up to £1000. Sunrise would cost me more especially if moving large amounts (PNB only charge £7 for up to £10,000).
This has been mentioned a couple of times already, though what has been highlighted is (at least for the time being) you won't be charged if you have a Cash Card account (non-visa Debit card)