Unfortunately, it depends 100% on the mood of the officer who pulls you over, which in turn depends on your attitude at the time.
In the ten years I have lived here, I've been pulled over many times for spot checks and once for speeding - the day after a speed limit sign was moved, so I wasn't on my own!
In all cases, you need to be as co-operative and helpful as possible and don't get annoyed - even if you are in a hurry and are late for something!
In that time, I've never changed my license to a Spanish one. In fact I still have the old A4 sized green paper driving license and have never had any problems when showing it to the police. The last time was a couple of weeks ago driving back home from Playa Paraiso.
It doesn't get you out of driving offences here entirely though as they have on the spot fines. They can't however put points on your license, though knowing the way things work here, they may well 'tot them up' if you are a serious offender and confiscate your car when your tally reaches a certain point!
What I have been told on many occasions though is that with a residencia as proof that you live here, you can't be done for driving offences in the UK - as there isn't an on the spot fine system there and all the police paperwork is set up only for UK residents.
I've never tested this theory and it's probably just a myth, even though it does sound plausible. Things could well have changed back in the UK.
Barrie