London landlords are selling up their buy-to-let properties at record rates as anticipated tax hikes from the U.K. Labour government add further pressure to the once lucrative investment sector.

Almost one-third (29%) of homes currently for sale in the capital were previously rented out, data published on Thursday by property portal Rightmove showed.

The spike mirrors a wider uptick in rental property sales across the U.K., where 18% of all nationwide listings were previously tenanted, according to Rightmove.

Rightmove said it was not yet clear that the figures pointed to a "mass exodus" by landlords, but rather to a gradual decline in the appeal of the buy-to-let sector. The previous five-year average of former rental listings for sale was 14%, while the proportion of ex-rental properties on the market in 2010 was 8%, Rightmove said.

It highlighted that it expected tax hikes in Finance Minister Rachel Reeve's forthcoming Oct. 30 Autumn Statement — including a possible increase in Capital Gains Tax (CGT) — to become a "potential driver" of the increased sales.