Originally Posted by
forextrader
You can spend it all - the "minimum" is £2.50, once over that each 50p is worth 120 miles.
Not sure if you get the bonus miles for "not whole" vouchers.
You can spend £2.50 of a £3.50 voucher though. When you go to convert, add £2.50 of vouchers then put in the £3.50 code, and you'll get £1 'change' redeposited back.