I just 'phoned the BT operator to enquire about call charges to this number, she told me it was not a BT number but a number given by torch communications, she thought the charge was about 10p per minute but wasn't sure. I couldn't find torch communications on google.Does anyoneone know about these numbers?

Trying to find out the cost of calls to these premium numbers is a complete nightmare.  It's just not simple to find out the cost of calls to 0871.  Trying to make sense of the BT Price List is almost impossible.  You have to check out two parts of their price list to get anywhere.

You need the more than just 0871 to find out the cost.  For example calls to:
0871 041 1xxx are charged at call rate i10 which are charged at 5.957p per minute (7p inclu VAT) at all times.
0871 400 xxxx are charged at call rate g14 which are charged at 6.808p per minute (8p inclu VAT) at all times.
0871 401 xxxx are charged at call rate g7 which are charged at 8.510p per minute (10p inclu VAT) at all times.

Go here to find the call type (ie. 0844 xxx / 0870 xxx / 0871 xxx etc) and here to find the calls charges.

These charges are from BT Residential Lines, there are different charges from Business & Payphone lines.  Hope this helps.