UPDATE 1-Moneysupermarket hit by First Plus decision

(Adds detail, market reaction)

LONDON, July 8 (Reuters) - Shares in British price comparison site Moneysupermarket.com Group PLc (MONY.L: Quote, Profile, Research) plunged by 17.4 percent on Tuesday after it said First Plus' withdrawal from the secured loans markets will impact sales.

Moneysupermarket said it will take steps to mitigate the impact of the decision by the Barclays' (BARC.L: Quote, Profile, Research) unit by sourcing additional capacity elsewhere, by reviewing costs and by reviewing loans advertising spend.

But the withdrawal from the market of the leading loans provider will reduce 2008 revenues by about 7 million pounds ($13.8 million) and wipe up to 5 million pounds from earnings before interest, tax, depreciation and amortisation, it said.

Shares in Moneysupermarket.com, which floated at 170 pence a share last July, had tested new lows of 72.5 pence at 1308 GMT.

Welsh-based First Plus, which provided second-charge loans allowing customers to borrow based on the equity in their home, will stop making loans to new customers from Aug. 9, it said earlier on Tuesday. (Reporting by Paul Sandle; Editing by Rory Channing) (paul.sandle@thomsonreuters.com; +44 20 7542-6843) ($1=.5065 Pound)