If a tribunal rules that you've been unfairly dismissed the employer MAY decide to reinstate you. However he is not obliged to. If he doesn't he will have to pay compensation.
This link is to a commercial site (which I'm not recommending) but the calculator should prove useful:
http://www.jobrights....missal-calculator.htm
General information here
http://www.direct.gov...Dismissal/DG_10026696
From what I've read elsewhere, it seems that the golden rule for having any chance of a successful claim for 'constructive dismissal' is that the employee must be able to show that they'd exhausted all of the usual dispute resolution procedures before they walked out.
Chris