The FTSE 100 was up 0.3 percent at 0933 GMT amid lacklustre volumes as the United States celebrated Thanksgiving, while the FTSE 250 was 0.2 pct higher, set for its third straight week in the red.
European Union negotiators will meet on Friday to try to clear the last hurdle before a Sunday summit is due to endorse the Brexit deal, but Spain's eleventh-hour objections over Gibraltar mean the final text might not be ready until the last minute.
"With Sunday's EU-UK Brexit Summit back on after yesterday's progress, any soundbites on remaining resolutions, be it actual progress or hopes thereof, as well as threats or actual spanners in the works, could keep GBP and thus the FTSE and its components on edge into the weekend," said Accendo Markets analyst Mike van Dulken.
Software firm Sage Group, up 3.4 percent, topped the FTSE 100, recovering from three-year lows hit earlier in the week following its results.
Housebuilders and banks also clawed back some ground lost in recent weeks amid the Brexit turmoil - Persimmon was up 2.2 percent and Lloyds Bank rose 2.1 percent.
The big moves were among the mid- and small-cap companies with M&A news driving Ibstock and Flybe.
Ibstock jumped 11 percent to the top of the FTSE 250 after it sold its U.S. brick business in a deal worth $110 million. The company said it will use the proceeds to repay debt. Peel Hunt upgraded the company to 'buy'.
Flybe shares took off after Sky News reported that Virgin Atlantic is in talks to buy the UK-listed regional airline a week after the company said it was in talks to sell itself.
The shares have lost two-thirds of their value so far this year as the company grapples with higher fuel costs, lower demand and a weak British pound.
A downbeat note from Jefferies pressured Ted Baker, which was the biggest loser among the midcaps, down 4.7 percennt.
Retailers were mixed as investors watched for signs of how much cash British shoppers were splashing on Black Friday discounts. Analysts say sales could help revive the high street's fortunes a little after a difficult year for the sector following a string of shop closures.
Blue-chip Kingfisher, Europe's second largest home improvement retailer, was down 1.3 percent, extending losses earlier this week after reporting weak quarterly sales in France.
Cantor Fitzgerald analysts cut their forecasts following the results, noting there will be no quick fix for the company's issues.
"Management believe they are on track to achieve their year 3 milestones, but as we have flagged before, execution remains key," they said.
Marks & Spencer was up 1.3 percent and penny stock Debenhams lost another 4.5 percent.