UPDATE 1-Rival says Gas Natural deters customer switch-paper

* Iberdrola say Gas Natural hampers client switchovers

* Gas Natural denies any wrongdoing

(Updates with comment from Gas Natural)

MADRID, Nov 2 (Reuters) - Spanish utility Iberdrola (IBE.MC) said it has complained to the country's competition body CNC that rival Gas Natural (GAS.MC) has made it hard for clients to switch to other gas distributors.

Iberdrola said it convinced 300,000 Gas Natural customers to switch over to it by making them an offer on the phone, but says its rival put obstacles in the way of the change-overs.

Gas Natural said it had not been notified of any complaint against it lodged with the CNC and denied any wrongdoing.

Iberdrola said the customers were households and small and medium-sized businesses, who can now choose their gas distributor after recent deregulation.

A Gas Natural spokeswoman said current legislation did not oblige operators to initiate a switchover to a rival operator when a request was made by telephone and not in writing.

Spanish consumer groups say electricity and gas deregulation has so far amounted to confusing offers from rival operators, aggressive marketing campaigns and limited savings.

(Reporting by Sarah Morris; Editing by Erica Billingham and Simon Jessop)