Back in 2013 I wrote a report for GWPF about the official UKCP09 climate projections and Nic Lewis's discovery that the underlying model was incapable of simulating a climate that matched the real one as regards certain key features of the climate system. The final predictions in UKCP09 were based on a perturbed physics ensemble: a weighted average of a series of climate model runs, each with different key parameters tweaked, with the weighting in the final reckoning determined by how well the virtual climate produced matched the real one. As Lewis revealed, since the climate model output couldn't match the real one, we were effectively being asked to believe that a weighted average of unrealistic virtual climates would nevertheless produce realistic predictions.
James Annan has an interesting post on the subject of UKCP09 here, making the point that there is now a lot of research that suggests that the whole perturbed physics approach is flawed anyway:
[It was] our series of papers on ensemble analysis starting in 2010 (eg here, here, here and here) that most clearly argued not only that PPEs had serious problems, but also that the MME was much better than previously believed.
So not only is UKCP09 fatally flawed but the whole perturbed physics approach to climate prediction is at best an also-ran in the climate prediction stakes.
The New Year's resolution for the Met Office is presumably to get back to the drawing board.