Britain's FTSE falters as M&S, Persimmon updates disappoint

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* FTSE 100 flat

* Consumer stocks, energy add support

* SSE (LSE: SSE.L - news) , Innogy to merge UK retail activities

* Trading update weighs on Persimmon (Frankfurt: 882058 - news)

* M&S shares also lacklustre after half-year results

By Kit Rees

LONDON, Nov 8 (Reuters) - The UK's top share index steadied on Wednesday as earnings were a source of weakness for Persimmon and Marks & Spencer (Frankfurt: 534418 - news) , though gains in heavyweight consumer goods firms supported the index.

Britain's blue chip FTSE 100 index was flat in percentage terms at 7,511.36 points by 1001 GMT, while mid caps retreated 0.1 percent.

More broadly, gains in big, defensive stocks such as Imperial Brands (LSE: IMB.L - news) and British American Tobacco (Kuala Lumpur: 4162.KL - news) , added the most gains to the index, while gains among oil stocks BP and Royal Dutch Shell (LSE: 0LN9.L - news) also helped.

Paper and packaging firm Mondi (Frankfurt: KYC.F - news) was among the biggest gainers, up 1.6 percent after Morgan Stanley (Xetra: 885836 - news) moved its rating on the firm to "overweight" from "equal weight".

A number of disappointing updates weighed on individual firms, however. Shares (Berlin: DI6.BE - news) in housebuilder Persimmon fell 3.4 percent, the worst-performing on the FTSE 100, after it issued a trading statement.

Shares in Marks & Spencer fell 0.7 percent after reporting results, which included another profit fall.

Grocer Marks & Spencer also said that it would accelerate its turnaround plan, and would open fewer Simply Food stores than previously planned.

"You've got a slightly weaker UK consumer possibly coming through in one or two of the retailers' results," George Salmon, equity analyst at Hargreaves Lansdown (Frankfurt: DMB.F - news) , said, adding that upcoming results from Halfords and Sainsbury (Amsterdam: SJ6.AS - news) would shed more light on this theme.

Shares in utility SSE nudged 0.7 percent higher after agreeing to merge its UK retail activities with German energy group Innogy.

SSE also reported half-year figures, which included an 8 percent drop in profit due to weakness in its networks business.

Some analysts were cautious about the merger announcement.

"Although the idea of a spin-off is understandable, we highlight that both businesses vary significantly in outlook and the industry's track record in integrating service and billing systems is poor," analysts at Jefferies said in a note.

"The move could also result in a rebasing of SSE's dividend and impairment for Innogy."

Outside of large caps, Wizz Air (Frankfurt: WI2.F - news) dropped 7.7 percent after reporting results, with the focus on concerns over ticket pricing trends.

Wizz Air's CEO also said that it was interested in acquiring airport slots at London Luton from failed airline Monarch.

(Reporting by Kit Rees; Editing by Raissa Kasolowsky)