I still read this as your in play bet is refunded if it loses, but it can't be larger than pre-match bet with a maximum if £50.
I've spoken to people who have done this before and that's how it works, hence why they call it a fantastic offer.
To qualify for your risk free In-Play bet, simply place a bet before kick-off, then once the game starts place another bet on any In-Play market. If your FIRST In-Play bet loses we will refund this stake, up to the same value as your largest pre-match bet (max £50*)
I'm sure someone on here would have taken advantage of this who can confirm?