Eomni,
Any one who takes an MPL course and would like to be able to fly single pilot for pleasure can do it pretty easily. The CAA will accept ATPL theory exams in lieu of PPL exams, so adding a PPL after completing MPL would be fairly easy. If the MPL syllabus includes a 150NM cross country during the single engine phase, I would imagine a PPL skills test with an examiner is all you'd need.
The MPL doesn't tie you to a single type or to a single operator (for example, most of the Sterling MPL's got picked up by Ryanair when Sterling failed), though the bond will achieve the latter. Last year, Flybe required their FTO's to guarantee that they would fund and deliver training to single pilot CPL/ME/IRMCC standard if Flybe went to the wall. I don't know if they are requiring it this year, but FTE's web site makes no mention of it this year.