Generally I think lots of them are over priced, especially Mothercare and Mamas and Papas! Kiddicare are great, really helpful and the toilets are hilarious! I've got lots of basics from Asda and bought some lovely stuff from Next in the sale.
Yes to Jojo Maman Bebe. Also joules is nice but IMO quite ££ for what it is and not a shop but mail order boden have nice baby bits. Also Toby Tiger have nice bits (look online) and I LOVE a brand called 'toto knits'.
If you mean for clothes definitely worth having a look in Tescos and Asda!
Also subscribe to zulily.co.uk they have offers on various baby designers - I'm obsessed with it! We don't even know what we're having yet but haven't been able to resist buying a few bits as the discounts are so good!
Mothercare - expensive and unhelpful M&P - expensive, style over substance and clothes/pushchairs tiny. Kiddicare - Good prices, fab deals, excellent mail order Jojo - Pricey, but excellent quality and their clothes are a but less ubiquitous than Boden. Good customer service too. John Lewis - superb, as with everything. Lovely baby/ Children's clothes, but come up quite small Ikea - great for kid's furniture and bits and bats - bibs, rugs, some toys, cutlery, step stools etc and the best high chair ever made. TKMaxx can have some absolute gems. Of the supermarkets, I like Sainsbury's best for clothes. Amazon can be competitive for big stuff.