How much would i get as a payout for wrongful dismissal?

my husband had been working with his employer for 5 months and was sacked 5 days before Christmas for 'poor performance' and no dismissal procedures was followed,he was signed off sick for two weeks prior to this, he knows that he can take them to a tribunal for wrongful dismissal but is unsure what payment he would or could get if he was to win the claim, if anyone could help?!?!