What is being discussed here is a grey area that many's a lad has disussed in the past without ever receiving a definitive answer. It's like an insurance urban legend. Insure a micra -drive a ferrari -almost sounds too good to be true..........
The key seems to be whether the vehicle in question has to be otherwise insured or not. The requirment for it to be otherwise insured effectively prevents this practice. However, what good, or what is the point of your third party extension if it does not actaully cover you to drive someone elses car (without conditions). I mean why should a car have to be covered under two policies -either your insurance covers it, or it doesn't? And if it doesn't then it isn't worth the paper it's written on. I don't have the definitive answer -just expressing an opinion.
In order to tax the vehicle in question it needs to be insured at the time of renewal (that is the official line).So you need to insure it properly at least for a while. Of course you could do it online and just lie, making up insurance details in order to get the tax disc, this is the data that feeds into the NPR system,I assume, so ok on that front (I do not advise or condone this behaviour, I'm sure you'd be breaking some kind of law, providing misleading information, etc).
That get's you a tax disc. Next you will ideally need an insurance disc -at least to keep the fuzz off your back. tranfer cover to the FTO, get a cert, transfer back. Most insurers will ask for the disc back -but I doubt they would actually follow it up if you don't return the disc. So visually the discs would be in order.
Remember, you are required to be insured -not sure if we have ticked that box or not, but you are also legally required to show a valid up to date insurance disc -having one that was valid (until you swapped cover and kept the disc, doesn't really cut it -technically at least).
Whatever about getting through check points uncheacked. The real issue arises in the event of a claim. If your GF legally owns the car, but had never actaully insured it -(at least for any meaningful length of time), and you are teh only driver, any insurance company is unlikely to pay out.
Of heard of young people driving cars under their parents name. The car legally belonged to the parents, but the real owner was the son/ daughter. In the event of an accident, the loss adjustor/ assessor, just makes some casual enquiries to neighbours etc about who owns and drives the car. Result -no pay out.
Insurance companies, now more so than ever will be looking to minimise their claim pay outs, give them the slightest opportunity and they will take it.
My suggestion would be ditch the Almera.