Id just like to thank the OP for bringing this to our attention.
I've just placed my free bet at betfred, I was browsing for odds and found a brazilian football match with bet odds of 7.0 and lay odds of 6.4, stupidly I used the £50 free bet on it... Whereas I have a feeling that if i'd used my own money I'd have made more cash due to the whole SNR crap. but anyway, its a high yield for lowish liability I guess so a decent bet. I was a bit confused by the "betting calculator", I think the liability box is wrong. I calculate the actual liability at betfair, and what you NEED TO HAVE IN YOUR ACCOUNT, as what the fundmydegree "betting calculator" has in one of the lower boxes for liability.
Can anyone confirm that the above is correct?