I think that, on the whole, restaurant price increases are being driven by price rises for ingredients, energy and labour rather than owner "greed". In decent-sized town centres, there's usually a reasonable amount of competition.
The exception might be PE-backed businesses where the playbook is to increase prices AND investigate scope for reducing quality (e.g. 6 mozerrella balls on your pizza rather than 5). Of course that's fine in the traditional PE "turnaround" situation where a business is losing money and change is needed - it's not so great when the business is doing OK but the PE house is just looking to ramp margin higher... I used to be a big Pret fan but the prices there are now absolutely insane (and I'm a reasonably high earner).
Agree with those who have highlighted the issues with the "deal" / voucher business model. Benefiting the well-organised at the expense of the cash rich/time poor (or the drunk

) isn't the worst thing that could happen but it leaves a nasty taste (boom-tish) when you realise you've been mugged relative to other customers!