Any costs incurred by someone's illegal act or negligent act can be recovered under English and Welsh law, not sure about Scottish.
But by just registering a domain name, the respondent hasn't done anything against civil law. If they have been trading against someones copyright, then this is against civil law and you will have a good case for recovering your costs.
But if you did try to recover your costs and the previous owner went to court to defend themselves, what would happen if the judge said he was right and the domain name should not have been handed over? You might be risking an almighty ongoing battle which could last further months.
I think that's why most just let it drop,
Although I don't know if you would have a case against nominet for letting someone register it without rights and then charging you £750 to get it back. They should have to hand the £750 back if it's found they have let this guy register it.
My bet is that these would be the best people to take to court, but better have some deep, deep pockets.
Mind you take them to the small claims court for £35 and even if you loose you don't have to pay their costs (as long as claiming under £5,000) worth a punt for £750
GW