All things considered I would recommend Stapleford Flight Centre. I say all things considered because I do have some negative things to say about the place, if you want to hear more about them then message me but they don't concern the quality of training. They use the Seneca for the multi-engine training and the DA42 for the IR which makes life a lot easier (which is what you want for the IR).
The Senecas are old and well used but they do the job. They can get you through the ME course in 3 days if you're a good enough pilot and you're not held back by the weather.
Their IR instructors are good and the quality of training is of a high standard. They have two DA42 sims and two aircraft which are both in constant use.
I passed CPL ME and IR courses on minimum hours with series one attempt one passes in all three tests (proves the school has the ability to get you through the course on target if you've the motivation, dedication and the skills required).
Contact Lisa for more information, shes a busy woman but probably the best thing about Stapleford from a students point of view.
Good luck.