This may not last forever, but so far there is no limit on the precept that can be charged by a parish council. Up to now, even with the present pressure on local authorities, the government has taken the view that local council precepts are generally too small to matter.
If you're thinking about your scheme to aid the "poor" of the parish, that does appear to be limited. I don't see a specific power to aid the poor, which means that you would need to use LGA 1972 section 137. Expenditure under section 137 was originally limited to £5 per elector. The figure has been uprated with inflation and last year reached £6.80. I don't know this year's figure offhand.