The UK now has a case against him, and a very strong one. He fled bail, and that is a crime. That crime is still ongoing since he's still fleeing said bail. So they can arrest and charge him for that. Doesn't matter if the original matter is log dropped, he is still on the hook for this.
That's the thing with court dates, bail, and all that jazz: Even if the case against you was going to be dismissed, if you skip bail you are now guilty of another crime. You have agreed to appear in court and a failure to do so is against the law.
The UK had no beef in this originally, they were just acting on an EU arrest warrant. Sweden said "We want this guy," the UK looked at the warrant and said "looks valid per the treaty" and thus arrested him. They had no interest or ability to decide on the validity of the charges, only if the request required them to act per treaty. It did so he was arrested, and then released on bail.
He challenged the extradition all the way up to the high UK court, but the courts found it was a valid request that the UK had to honour. Nothing to do with his guilt, just that the request was a valid one and they were bound by treaty to hand him over. Had he gone to Sweden then, that would have been the end of the UK's involvement. His bail would be returned and the UK would have no further interest in what happened.
However he fled rather than handing himself over. So at that point, he became a fugitive in the UK. They now have a case against him. It is totally separate from the original case, it is simply a case of skipping bail.
Likely they'll want to act on it too, since he's been flaunting it in their face for years.