Hello Scott,
With any uneven tread wear, the first port of call must be to have the car thoroughly inspected for wear. Actually adjusting the alignment must be the last job. The logic is:- when the car was new, the alignment was factory set so that the tyre wear would be even, so if you rears are wearing (grossly) uneven, then obviously something has changed - the adjustment cannot move).
Yes, you can have 4 wheel alignment carried out, but simply adjusting without a thorough check will be a complete waste of money. It’s not uncommon for front alignment to be out, but rear - less common - broken springs??
Who to do it? There are plenty of tyre outlets/ garages who have the sophisticated equipment - using it properly is another thing! - so choose carefully.
Where in Wales are you - it’s a big place.
Kind regards,
Gareth.