I have not yet declared this
Hurry up, you haven't got long.
All is not lost (pun intended). Losses made since 1996–97 must be notified to HMRC within four years of the end of the tax year in which they were made. So you are within that time limit for 2008-09 and 2009-10, notwithstanding the fact that such losses should really have been shown in the CG pages of the relevant tax returns. I would show the losses in your 2010-11 tax return and just accept the fact that you are more likely to face an enquiry into that year's tax return. As long as the losses can be satisfactorily evidenced, you shouldn't have anything to worry about.
Remember that brought forward losses are used in full or (if lower) to the extent that the gains of the year are reduced to that year's annual exempt amount.
Hurry up - you've got just over 4 hours!