LONDON (Reuters) - Home improvement costs have risen by a fifth, new data shows, as cheap and reliable Eastern European tradesmen leave the UK.

The rising costs of transport and raw materials, coupled with a shortage of tradesmen, have pushed up the price of improving properties by 20 percent over the past two years, according to the Royal Institution of Chartered Surveyors' Building Cost Information Service (BICS).

That compares to an eight percent increase in average wages.

BICS said homeowners no longer had a glut of quality European tradesmen to choose from, as an increasing number of central and eastern European nationals have returned to their native countries.

Half of the estimated one million British-based Poles have recently left the UK, according to estimates, a factor that has increased competition and pushed up costs for labour. In addition, the upward trend in oil prices is fuelling transport costs, while global demand for raw materials remains at an all-time high as emerging economies such as China and India show no signs of slowing down.

Taken together, these factors have pushed roofing costs up by 26 percent since 2006, plumbing and electric work by 22 percent and painting by 17 percent.

Joe Martin, executive director of BCIS, said many homeowners were, nevertheless, opting to improve rather than move amidst the current housing market downturn.

"Many are choosing to stay put and renovate or extend in order to upgrade their property rather than taking on more debt in a falling market," he said.

"This can be a wise strategy as home improvements add value to a property, and people will be well placed to take advantage of this uplift in value when the market shrugs off the current slump."