"I'm fed up seeing friends who are contracting wriggling out of paying their fair dues in tax."
Do something about it then!
"Many of my contracting mates have more security than the permanent staff they work with e.g. minimum contract notices of 2 months or more, compared to 1 month or less for the permies."
I've Never seen a contracting contract with more than a months notice clause on the part of the employer/agency, and a contractor normally has no get out clause/notice period. They also get no redundancy pay or any other such benefits.
"Contractors often work in the same offices, for less hours as the permies."
Usually because they are contractually only allowed to work set hours. Over time is not paid or had to be signed off and permanent staff are given priority. Not a lot of point working for free as there is no possible future gain for it (promotion etc).
"Many of the ones I know use receipting / expense ruses to claim back the cost of mileage, car leasing, plane ("business") trips with spouses etc. I'm fed up of my mates asking to keep the receipt when we eat out so they can claim it back as a 'cost' despite the meal having sod all to do with their day job."
Mileage and leasing are not illegal as long as the normal benefit in kind is paid just as if it where a permanent employee with a company car. If they are making false mileage claims on a personal car or flights that are not relevant that is just fraud. The same on the meals in most cases it is fraud and should be treated as such.
"Why should contractors who often earn 2-3 times as much as the permanent peers per hour pay 1/4 -1/6 in tax?"
If they are then they must clearly be breaking the rules. Have you any actual figures to back this up as in 10 years of being a contractor I never managed anything like this but then I was honest and reasonable.
"They never seem to get caught out by HMRC, and having seen my own tax rise year on year I don't see why I should pay more towards their healthcare, the education of their kids and the social care of their elderly parents than they do at the expense of being able to provide for my own family."
Bloody simple, stop moaning and grass them up if it really pisses you off. Just like benefit fraud, fraud is fraud and they are breaking the law. If you are so sure of your facts and so annoyed by it do something about it.
If you must know as a contractor I was pissed off when other contractors did this and I played it straight and paid all the taxes, what pissed me off even more was when they then complained when they got caught. Even after fines they were better off than me.
If you want to know who is really ripping the country off, check out mps, last time I looked they got double the mileage allowance of any other person in the UK for 'business' miles and are allowed £20k in living away expenses (£0 for contractors).