That's a 'neat' piece of journalism!
The Telegraph hasn't got any actual figures (or even any official confirmation of a price rise) but they've got someone to make a guess:
" . . . widely respected City analyst, Peter Atherton of Liberum said an 8 per cent rise sounded "about the right level" given the rising cost of environmental levies and transmission charges".
They've then done their sums to come up with this statement:
"A jump of 8 per cent would push British Gas bills up to a record of almost £1,450, when paying by cash or cheque".
That conveniently ignores:
(a) the fact that the 8% figure appears to have been plucked out of thin air ; and
(b) most people don't pay by cash or cheque anyway (as they favour direct debit, which lowers their bills)
http://www.telegraph.co.uk/finance/personalfinance/consumertips/household-bills/10322826/British-Gas-to-raise-bills-by-100-to-record-levels.html
Read with caution!