This answer makes two assumptions:
1. I'm assuming that your age is between 65 and 74.
2. I'm assuming that your pension is your only income. (i.e. I'm assuming that you're not receiving untaxed income from savings, share dividends, etc)
The tax man allows you income of �7280 per year before Income Tax cuts in. This is equivalent to �140 per week. So, if your pension is �63 per week, you're allowed to earn an additional �77 per week before tax cuts in.
Note that the first �2150 of taxable income only attracts tax at a rate of 10%. That's about �41 per week, which will only require a tax payment of about �4 per week. (i.e. if you earn a total of �118 per week, you will only lose about �4 per week of this in tax.
Chris