Hello, welcome to the forum.
On the basis that middlesex probably doesn't exist I'm not sure where you are, but I live in Ealing, which was also middlesex. There are a few places near me to skate but I mainly go into central London. Where are you based?
Assuming you are far out west, If you live near Hayes why not try http://www.hillingdoncyclecircuit.org.uk/
at Minet Country Park, where Uxbridge Road meets the A312. Alternatively, if you are further out towards Staines then people have used Dorney Lake, but I haven't, so can't comment
Anywhere nearer to London than Staines or Hayes gives you the perfect opportunity to skate in central London. there is a group called the Easy Saturday Skate who meet at Battersea Park who do a few laps on Saturday morning and meet up at a reasonably slow pace. You can find them here: http://www.easysaturdayskate.com/about.html