Now that the trial's over and a 34 year sentence passed, one hopes an intergovernmental agreement can be reached for Mr Mann to serve his sentence in a UK jail. Given that Mr Mann was on his way to Equatorial Guinea with the intention of murdering people I can't think many people would regard the 34 year term excessive. An exchange agreement to allow him to serve the sentence within reach of friends and family in the UK makes sense only if the agreement kept him in a high security jail where he would be less likely to abscond or be broken out by his adventurous one-time colleagues. Parole for the second half of his sentence might even be acceptable so long as he's considered genuinely penitent.
http://news.bbc.co.uk/1/hi/world/africa/7470762.stm
http://news.bbc.co.uk/1/hi/world/africa/7493717.stm
One hopes Equatorial Guinea has issued an international arrest warrant for Sir Mark Thatcher, given all the new evidence that's come to hand.
One hopes that a part of any agreement with the UK for Mr Mann serving his sentence here would be a guarantee to extradite the plotters still at large if they came within UK jurisdiction.