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* Department stores Christmas underlying sales up 5.1 pct
* Department stores boss confident firm outperformed rivals
* Waitrose underlying sales down 1.4 pct
* Group profit guidance maintained (Adds detail, comment from department stores MD Andy Street)
By James Davey
LONDON, Jan 6 (Reuters) - Britain's John Lewis Partnership maintained its full-year profit guidancethanks to a strong Christmas performance from its departmentstores which reported robust fashion sales despite a mild startto winter.
The department stores helped to offset a more subduedperformance from the group's upmarket supermarket chainWaitrose.
The John Lewis trading statement also contrasted sharplywith one from clothing retailer Next which began thepost-Christmas reporting season on Tuesday with a disappointingupdate. Next blamed Britain's unusually warm weather in Novemberand December for a sharp slowdown in sales growth.
The John Lewis Partnership, whose worker co-ownership modelhas been lauded by Prime Minister David Cameron, has been thestar performer of Britain's retail sector for the last sixyears, helped by a strong online operation and modern stores,many of which are in the more prosperous south east of England.
The group said on Wednesday that sales at Britain's largestdepartment store chain increased 6.9 percent year-on-year to 951million pounds ($1.4 billion) in the six weeks to Jan. 2 andwere up 5.1 percent at stores open over a year.
All three of its main product areas showed good salesgrowth, with fashion up 6.1 percent, home rising 5.1 percent andelectricals and home technology increasing by 9.6 percent.
Marks & Spencer, Britain's biggest clothingretailer, will update on Christmas trading on Thursday, withanalysts forecasting another decline in sales.
"The difficulty in going second in the (Christmas) results(reporting) is we don't know others yet. But I suspect when theink is dry our fashion result will look really good against themarket," John Lewis Managing Director Andy Street told Reuters.
The department stores' overall online sales increased 21.4percent over the six weeks, representing 40 percent of totalsales. Store sales fell 1.2 percent.
Waitrose's gross sales, excluding fuel, were 859.8 millionpounds, up 1.2 percent compared with last year and down 1.4percent on a like-for-like basis.
Waitrose noted that peak festive trade came particularlylate and was more concentrated than usual in the last daysbefore Christmas. Three of Britain's major supermarket groups,Tesco, Sainsbury's and Morrisons, aredue to update on Christmas trade next week.
Total John Lewis Partnership sales rose 4.1 percent to 1.81billion pounds.
"This has been a strong Christmas trading period for thePartnership despite the non-food market seeing significantshifts in trade patterns and the grocery market continuing to bechallenging," said Chairman Charlie Mayfield.
He said expectations for profit before partnership bonus,tax and exceptionals for the year Jan. 30 2016 remain unchangedat between 270-320 million pounds versus 342.7 million poundslast year. ($1 = 0.6833 pounds) (Editing by Kate Holton and Keith Weir)
