Trishtrash, there is no legal minimum or maximum requirements for tempretures. however the HSE recommend the following:
Indoor workplaces
You must provide:
a reasonable working temperature in workrooms usually at least 16�C, or 13�C for strenuous work (unless other laws require lower temperatures);
local heating or cooling where a comfortable temperature cannot be maintained throughout each work room (eg hot and cold processes);
thermal clothing and rest facilities where necessary, eg for �hot work� or cold stores;