the £100 a week is just a rought guide , if you've got £2k+ in savings and your bank balance is not going down each month you shouldn't have a problem with this.
anyway its about £100 a week after you've paid your rent and poll tax (if i remember correctly) but thats mainly used by some appeal judges, you dont have to have £100 spare aweek ! , the £100 figure is used by some appeal judges becuase its what a couple would get in social security benefits, so some use that figure at a guide.
the more money you can get the better, dont over do it, they might wonder what your living on, just try to make sure your out goings are not more than your incomings! and you shouldnt have a problem