Mr Brown rejected simplifications to the CGT system in 2001

Alistair Darling announced last month that CGT would be charged at a single rate of 18%.

However, in June 2001 the government held a consultation on CGT reform which considered the simplification that has now been adopted.

The Treasury's response at the time was "the government was not attracted by any of these proposals".

One of the main effects of Mr Darling's simplification of the CGT system was the abolition of taper relief.

Taper relief was a system introduced by Mr Brown in 1998 under which assets that were held for a long time were subject to a lower rate of tax.

"Now we have unearthed the latest critic of the government's ill-thought-out business tax increases - Gordon Brown himself," said shadow chancellor George Osborne.

A Treasury spokesperson said in a statement that the difference was that the 1998 reform followed "years of macroeconomic instability and under-investment".