UPDATE 1-U.S. rig contractor Ensco plans to rebase to UK

* Ensco to move domicile from Delaware, execs from Dallas

* Removal from U.S. indexes looms, Ensco shares down 1 pct

By Braden Reddall

SAN FRANCISCO, Nov 9 (Reuters) - Ensco International Inc (ESV.N) is setting off on what is now a well-worn route to Europe for oil and gas drilling rig contractors, by laying out plans to relocate its corporate headquarters to the UK.

Ensco said achieving a global effective tax rate comparable to rivals was one reason for the move, along with improved access to both European institutional investors and its clients outside the depressed North American drilling market.

While larger rivals Transocean Ltd (RIG.N) and Noble Corp (NE.N) chose Switzerland when they moved in the past year, citing similar reasons, Ensco said in a statement that it already had substantial operations in Britain.

Ensco's company domicile will shift from Delaware, while most of its top executives will move to Britain from Dallas.

This marks a reversal of fortune for the Texas city, which in the past four years has seen big U.S. companies such as Fluor Corp (FLR.N), AT&T Corp (T.N) and Comerica Inc (CMA.N) move their headquarters to the Dallas area.

Transocean and Noble both moved their domiciles from the Cayman Islands, which analysts put down to the relatively better protection provided by Swiss tax treaties if the U.S. government cracks down on offshore earnings. [ID:nL9640866]