I suspect you could probably save a fair amount each month by doing a few simple things:
1. Ensure that any vendor you purchase services from has you on the best rate. That includes things like gas and electricity, mobile phones or any other regular payment. In some cases you may have to threaten to leave, but in almost all circumstances you can reduce your costs by switching to a cheaper provider or demonstrating an intention to leave to your current provider.
2. Refrain from impulse buying. If you see something you like in a shop, go home first and think about it. If you still want it, go online and you'll likely find it cheaper, even with a delivery charge. If you don't really need or want it, you'll save a fortune!
3. If you spend a fair amount of money on fuel, sign up to petrolprices.com. You can check for the nearest and cheapest prices. You won't save more than a fiver or so a month, but every little helps!
4. Do as much purchasing as possible using a credit card with cashback. Again, you won't make millions, but it's free money. If you earn over £30,000/yr and spend a fair amount, get an American Express card, if not then use an Egg Money card.
5. Ensure that your debts are in the cheapest place possible, and that ANY savings you have go towards paying these off. Saving rates are far far less than debt rates, and you'll be just burning money in most circumstances. You can balance transfer credit card debts to a 0% card for a small fee, but you won't be charged any interest for a year or more. If you are paying minimums, then most of your payment will be interest, so you can then start paying it off rather than perpetuating the debt. If you have a lot of credit card debt that you don't think you can easily repay, consider a consolidation loan. A personal loan interest rate will be much much lower than a credit card, and your payments will go towards paying it off rather than the bank's money chest.
Lots of useful information here:
http://www.moneysavingexpert.com
I'd be surprised if doing the above you couldn't save net gain than £100 a month, unless you have things very well set up as it is.