I did SE/IMC rather than ME/IR with them but used Billins Air Services recently, next door to Bonus at Cranfield.
They have a Seneca, although I can't see a price for it on their website - I imagine that a quick email would resolve that.
Having trained with both Bonus and Billins for ratings, I was very happy with both training standards and examiner attitude at both, and Cranfield is good for IMC/IR training, having just about every approach you've ever dreamed of on the doorstep. Billins however was cheaper with better instructor availability.
If you want web links...
Billins:
Billins Air Services - Learn to fly in Cranfield for customers around Bedford, Milton Keynes, Bedfordshire, Buckinghamshire. PPL, Vouchers and much more
Bonus:
http://www.bonusaviation.co.uk/