I have a plan with Bristol Street - 3 years servicing (60,000 miles) for £24 a month over 32 months. The dealer I bought the car from wanted £37.50 ish over 36 months!!
I live in the North East and contacted all the VX dealers in the patch as a customer for the first service and was quoted between £250 and £296 (they all said 1st and 3rd service was the same price). I did the same for the 2nd service and £380 ish was the average.
One thing I will say is the price of plans vary and I was told that there is a laid down price plus the dealers labour charges, which dealers can then offer discount with the alleged maximum being 24%. I was quoted a price from Evans Halshaw and Bristol Street beat it by giving the 24%. You also qualify for a load of other so called benefits and discounts by having a plan but whether they are worth anything in the real the word is to be seen (10% parts discount, free tire repairs, collection and delivery service etc....)
I went for the plan so I know what the cost will be over the 3 years, however, come the time if there are any offers on the go, the plan will be cancelled as it is really just a glorified savings scheme with a chosen dealer!