I'm with M&S and because I live In London it's much more than if I didn't - it works out at roughly £209 annually or £17.50 a month. This figure is with no excess though, and I think it's nearly £7 per month cheaper if you don't live in London.
I went with M&S because it was recommended on here, but was a bit surprised it was so much more cos of where I lived.
Our vets are trained to sell Pet Plan that looks at specific London post codes, not just the general area. Goodness me, then did I think M&S was a bargain. For the platinum standard which provides up to £8000 cover per year (as opposed to M&S's £7000) but does have an excess where mine doesn't, it was FIFTY POUNDS SOMETHING A MONTH!!! They rather generously deduct £3 off if you insure an additional pet (i.e. dog 1 = £50 per month, dog 2 = £47).
The vet's assistant which goes through the insurance, said she had only been trained on Pet Plan therefore was only legally allowed to promote pet plan.
I told her I was actually planning on getting M&S, and she took her name badge off, put it in her pocket, and said 'as a pet owner I would highly recommend them.'
I think Axa is behind both M&S and Healthy Pets though.