LONDON, April 29 (Reuters) - Travis Perkins, Britain's biggest seller of building materials, said on Friday its forecast for materials price inflation, which it had expected to ease into the second half of the year, was now more uncertain.

The group, which trades from over 700 branches in the United Kingdom, said increased prices were likely to form a higher proportion of sales growth across the year than previously thought.

Travis Perkins' total sales for the three months to March 31, its fiscal first quarter, were 13.6% ahead of the same period last year when COVID-19 restrictions were still in place.

Total sales in the merchanting division were up 17.9%.

"Pricing accounted for approximately two-thirds of the growth with manufacturer increases continuing to be passed through (to customers) in an orderly manner," the group said.

Travis Perkins' expectations for the full year were unchanged.

It said order books remain robust across UK construction, underpinned by the UK's backlog of infrastructure work, the ongoing requirement for new housing and growing interest in energy efficiency projects due to the hike in energy costs.

It said the construction supply chain had largely normalised by the end of 2021 and, although the war in Ukraine and the subsequent impact on the global economy may impact that stability, stock levels were healthy.

Shares in Travis Perkins, which last year spun out its Wickes home improvement business, have fallen 18% over the last year. ($1 = 0.7983 pounds) (Reporting by James Davey, Editing by Paul Sandle and Elaine Hardcastle)