i don't understand why they would temporarily fix it, it would take a few hours to take the head off and inspect it, then to just botch it up and put the had back on would take a few more hours,he must be a right c*nt considering he might well of done that, any normal person would of sourced a 2nd hand head after spending time investigating the problem, it just aint worth botching it up considering how much it would of cost, a new head set costs 60 quid - u can source a 2nd hand head for a few hundred fgs - u looking around 250 - 300 to get a used head with a new head set and for a garage they dont even have to pay for labour
he prob got it in part exchange on the cheap and found it had a problem then botched it up and got rid
for you to sue him you have to prove the car was not road worthy and that he has breached the sales of goods act in terms of accuracy at the time of selling the car
now a head gasket could go any time and you will have trouble proving he carried out the work to botch it up, it gonna cost u 85 quid to take him to a small claims court
my advice would be to admit that you have been had, like well all have at one point in our lives when buying 2nd hand cars and move on