UPDATE 1-Utilities withdraw from UK offshore tender -sources

* RWE, ESB, Statkraft and StatoilHydro pull out -sources

* Ten bidders now left in the auction-sources

* Move deals blow to UK offshore wind plans

(Adds company statements, detail)

By Greg Roumeliotis, European Infrastructure Correspondent

AMSTERDAM, Nov 25 (Reuters) - Four energy firms have withdrawn from a 1.15 billion pounds ($1.9 billion) auction of UK offshore electricity grids that aims to attract private capital in connecting offshore wind farms, sources said.

RWE RWE.DE, ESB International, Statkraft and Statoilhydro have pulled out of the process either because they found the structure of the scheme unattractive or because they don't want to buck the European trend of separating generation from supply, two sources close to the process said.

"The regulations on this have proved to be more complicated than expected, and therefore we have terminated the process," a Statoilhydro spokesman said.

Regulator Ofgem has communicated to the remaining bidders that the four companies have pulled out of the tender ahead of Dec. 14, when a shortlist is due for each of the nine Offshore Transmission Owner (OFTO) projects on offer, the sources said.