Britain's FTSE rises as Sainsbury's, Morrisons gain

* FTSE 100 up 0.6 pct

* Sainsbury (Amsterdam: SJ6.AS - news) outperforms over Christmas period

* Mid-caps Morrisons and Debenhams (Other OTC: DBHSF - news) surge on results

* Housebuilders benefit from sector upgrades

* Miners, Sports Direct fall on downgrades

By Kit Rees

LONDON, Jan 12 (Reuters) - UK shares advanced on Tuesday, pulling back some of the previous session's losses as upbeat industry data for Sainsbury's and encouraging results for mid-cap grocer Morrisons boosted the supermarket sector.

Sainsbury's shares rose 2.3 percent, defying industry data showing that British retail spending over the festive period recorded its weakest quarterly growth in more than a year.

Figures from market researcher Kantar Worldpanel showed that Sainsbury's performed best out of the major players among the grocers over the crucial Christmas trading period.

Shares (Berlin: DI6.BE - news) in fellow grocer Tesco (Xetra: 852647 - news) also received a leg up, advancing over 5.1 percent.

The UK's blue-chip FTSE 100 index gained 0.6 percent at 5,906.64 points by 0938 GMT, slightly underperforming the broader European market.

There were positive industry figures among mid-cap retailers too, with department store chain Debenhams surging over 14 percent after reporting a rise in sales in the Christmas trading period, although some investors remained unexcited by the company's results.

"Debenhams' trading update was reassuringly unremarkable. With (Other OTC: WWTH - news) its busiest trading period behind it, the business remains on track to deliver profits in line with expectations," David Stoddart, analyst at Edison Investment Research, said.

Likewise, Britain's fourth-largest supermarket Morrisons beat analysts' expectations after posting a rise in like-for-like sales, ending three years of declines and sending shares 10 percent higher.

"With better than expected results, Morrisons strategic priorities are still to stabilise the business and return to profitability ahead of sales growth. However, Morrison's still face several challenges heading into 2016," Simon Johnstone, researcher at Kantar Retail, said in a note, citing sectoral woes including a price war due to the rise in popularity of discount grocers.

Also among top risers on the FTSE 100 index were housebuilders Berkeley Group, Barrat Developments , Persimmon (Other OTC: PSMMF - news) and Taylor Wimpey (LSE: TW.L - news) , all gaining between 1.7 and 4 percent following a smattering of sectoral upgrades from Jefferies after Taylor Wimpey reported an increase in sales on Monday.

Jefferies said that it expected sector shares to outperform the UK large-cap market in 2016 as supply was unlikely to catch up with booming demand.

At the bottom of the blue-chip index, however, were British miners as downgrades hit BHP Billiton (NYSE: BBL - news) , which fell 3 percent, pulling down its peers in a troubled sector. Glencore (Amsterdam: GX8.AS - news) , Antofagasta (Other OTC: ANFGF - news) and Rio Tinto (LSE: RIO.L - news) were all down between 3.2 and 1.9 percent.

Sportswear retailer Sports Direct also suffered from broker downgrades from Numis and Haitong Research, falling more than 4 percent. (Reporting by Kit Rees, Editing by Ed Osmond)