B&Q must be loving this, yes the likes of The Range, B&M and home bargains sell some DIY stuff it's not as extensive as B&Q. You do have Toolstation and Screwfix but you can't browse one of them like you can B&Q and anyway Screwfix and B&Q are owned by the same people so not really competition.
Toolstation are also owned by Travis Perkins.
A word of warning about B&Q, they’re now using their website as a ‘fulfillment platform’ meaning other people get to sell stuff through it. So if you see a product on there, don’t expect to find it in store, a mistake I made recently. It’s quite misleading.
Wickes has been quite handy for me, but my local one closed down earlier in the year because the lease ran out and the site is going to be redeveloped. I think they're looking a bit run down and wouldn’t surprise me if they disappeared in due course. Wilko was also really handy for bits and bobs and were usually conveniently sited in normal city centre shopping areas, that’s left quite a hole. I’m a building manager and having Wilko about three minutes away on a bike was extremely useful. There’s a Toolstation about the same distance but you can easily queue for 20 mins at busy times, understaffed and slow service, and sometimes you just need to see the item to be sure it’s what you need.
I’ve found buying some DIY tools and materials online occasionally very frustrating, often crucial dimensions are not given, and the search facility on some websites is risible (Amazon possibly the worst, no idea how they’re so succesful)