I know HIFX are linked with Select, but I have been using HIFX for years and for property related transfers to other countries, so they should be acting independently.
It is always worth checking the market rate just before you talk to them, then you will understand the premium they apply.
You can get the market spot rate from
Yahoo! Finance UK - FTSE, Stock Exchange, Mortgages, Loans & More
and type in gbpaed=x where it says "Enter Company or Symbol"