Reading this Simster I think you think that the First pre match bet you place has to lose in order to get the free in play bet (Bit of a mouthful but think it makes sense), it doesn't, You just have to MAKE a bet pre match, it's outcome is immaterial, in order to get a free £50 in play which is refunded (about an hour after) if you lose after the match.
Personally I'd Bet on +0.5 goals, back the 0-0 as a cover so you are in a no lose situation as you described. Then, in play I back next goalscorer. It's a lottery but as I see its a free 50 quid (well, it will probably cost you £2 or so in the above situation but anyway) and you may as well try and win big with it. Nothing ventured and all that. As the £50 is refunded there is little point backing something at short odds.
You're right! Thanks for the explanation. So bet on +0.5 goals, cover it at Ladbrokes and then make whatever bet you like with the free £50. LIKE.