What others spend isn't particularly relevant as everyone has different family sizes, budgets, requirements and priorities.
Best thing to do is really review your budget to make the best overall use of your incomings and outgoings. Have a look at the budgeting section of moneysaving expert and get the weekly email for ongoing tips on making the most of your money.
As for where you shop, Asda or Morrisons are probably the cheapest online shops but I disagree with only buying toiletries etc when you run out, from these shops, the cheapest way is to always buy own brand, or branded on offer, and always buy ahead when you see an offer so you never have to pay full price.
Plus buy bigger packs of toilet roll when on offer as the price per roll can be half that of buying a small pack as and when.
Also think outside the box. One thing that surprises me on 'how do I spend less on shopping' threads is that no-one ever seems to mention the shopping trolley.
If you live in walking distance from an Aldi or Lidl but too far to carry shopping, if you have a shopping trolley it will pay for itself in no time at all compared to doing all your shopping at a more expensive supermarket and paying for delivery. Plus it's free fresh air and exercise.