Hi Eddie.
>>>Is there a legal way he can get out of being guarantor ?
No. If there was, guarantees would be worthless.
The first thing your neighbour needs to do is to accept that he'll have to pay the money back. However that doesn't mean that he has to pay it back at the same rate that the original debtor was meant to. He should cancel the direct debit with his bank and then write to the lender. That letter should acknowledge the debt, but also explain his current financial situation and offer to pay a nominal sum (perhaps £5 or £10 per month) until such time as his circumstances improve.
On receipt of such a letter many lenders will freeze the interest and accept the lower payments (possibly after requiring that a full financial statement to be submitted). They don't so out of any great generosity towards debtors; they simply accept that 'you can't get blood out of a stone'.
If the lender decides not to accept the offer of lower payments, all they can do is take your friend to court to seek a County Court Judgement against him. The judge would listen to his circumstances and make an order requiring your neighbour to repay the money at a rate set by the judge (and, importantly, at a rate which your neighbour can actually afford). As long as your neighbour then keeps those reduced payments up, there's nothing further that the lender can do.
Chris