Depends on what your intent with that currency value is.
Personally, I'd leave it as a double (to store decimal values) or maybe even an integer (assuming any decimal place is multiplied out by its associated tens place). Reason for keeping it numeric: You might wish to do currency conversion. You might wish to add this field up and have a total (maybe total per week, month, year, etc).
Now also remember the database is for data storage. Not for making data look pretty. That's PHP's job. To automatically add the £, you'll need to have PHP do it whenever it displays the price. Or, you can use MySQL's CONCAT() function to prefix the £ before the price value. That would work too.
