1. MOT testing. I think the British system is rubbish. Loads of small independent garages in cramped conditions with an axe to grind? I like the Spanish system. Clean, modern government run places, plenty of parking. Nice waiting rooms, efficient. You can book online (and choose your time slot and day) or over the phone. They only have a few per county but still plenty to choose from.
I agree that a conflict of interest could occur with garages doing MOTs. I have no experience of any other system although I have friends in Northern Ireland who curse the system there, which is along the lines of government-run test centres as you describe.
I suspect to implement such a system across the UK the cost of a test would spiral out of control.
Garages take on work to cover most of their overheads so the cost of doing MOTs is the (not inconsiderable cost of) space plus the equipment required plus one or more testers, VOSA fees, etc. Resources which also bring in business when they are testing, and can carry out repairs and servicing when not. They can be seen as a sales / marketing overhead so the true cost is probably not passed on to the customer.
I suspect government run centres would have to be heavily subsidised (motorists subsidised? - not going to happen) or charge a lot more than the current (not desperately cheap) £50 odd a go.
Personally, I have found a small, local independent garage who are honest and reasonable yet thorough, don't discount the standard test fee but then don't find faults simply to bring in work, so the current system works fine for me.
2. The law is very clear on legality of cars in other countries. The car must be legal in the country it is registered in. e.g. a Brit car in Spain must be taxed, MOT'd in Britain and insured. If you have it here for more than six months you need to convert it to a Spanish plated car. I presume the same rules apply in Britain to a Portugeuse car. However no one really knows or cares. One of my pet hates as it all potentially hinders labour movement arounbd the EU.
The problem being the authorities in the UK have no idea what standard a Spanish car should be maintained to and vice versa....
They do those road stops here in Spain. I have seen two. The concept is simple. They set up a heavily manned Roadblock(including a guy armed with a stinger itching to use it) on the motorway and stop every vehicle and look at documents (which here you must carry - should be the same in other countries too including GB). Then they close the roadblock when there is about TWO hours tailback and let everyone go with fines as appropriate or impounding for dangerous vehicles, drunks..
As I said, it would cause uproar in the UK, hence we rely more on regular testing.
I don't see the point in carrying documents in the UK. I can be required to show them at a Police station if necessary. Why should I carry them? I'd rather they were safely "filed" at home. (Anyone who's seen my "filing system" please stop chuckling!)
Besides, Police will believe the PNC and/or a phone call to your insurer over and above any documents you carry which might relate to a cancelled insurance policy, or be forged, etc. We have moved on from paper documents being any use, IMHO.
Kevin