Of course he would not venture into a UK jurisdiction ... and why should he?
If he sues the McCann's for loss of earnings it will be in a Portuguese court ... but he will be expected to prove exactly how much the alleged losses are ... which will require transparency of his finances over the period for which he is making the claim.
He may be relaxed about that ... on the other hand he may not ... and there is also the possibility to be considered ... that he may not necessarily win any action he takes against the McCanns.
Indeed..its just back on the roundabout again isn't it. They pay his costs, he sues unsuccessfully, pays theirs, etc etc. Really its nothing buy another payday for the lawyers. I'm sure he is sick of all the court crap now, and honestly..whatever you believe happened to Madeleine.. the McCanns are still surely racked with guilt and going through hell anyway even without the endless court cases all of this. Time it was all left to rest really.
(court cases, not the search)
I also don't think he lost earnings through them at all tbh, if anything he has profited from the case given the income from the book. Yes his 'good name' may have been called into question but launching another case is just tit for tat rubbish I think.