UK shares remained little changed due to a lack of major drivers and as deals were subdued in thin trading ahead of a Christmas holiday break.
The FTSE 100 .FTSE traded flat by 0900 GMT, still hovering around a near five-month high hit in the previous session, as oil majors Shell (RDSa.L) and BP (BP.L) benefited from firmer crude prices and offset a drop in exporters such as BAT (BATS.L).
The mid-cap FTSE 250 .FTMC is on course to rise for the fourth straight month, buoyed by lingering optimism around a smooth Brexit after Prime Minister Boris Johnson's election victory.
Dealers seemed content to reflect on major developments of the month, including a breakthrough in US-China trade talks and Johnson's victory, which triggered a rally in stocks leading up to Christmas.
Some of that momentum eased after Johnson's hard line on a trade agreement with the European Union revived fears of a chaotic Brexit and traders are likely to hold off on making further bets before gaining further clarity on both fronts in the new year.
But the exporter-heavy FTSE is still on course for its best month since April 2018, while the more domestically-focussed midcaps are on track for a fourth straight month of gains and their best since January.
The FTSE 100 looks set for its biggest annual gain since 2016, when Britain voted to leave the EU. The FTSE 250 is on course for its best year since 2013, as several long-standing hurdles to Brexit have now been removed.
Among major decliners, NMC Health Plc (NMC.L), which rallied almost 37 percent on Monday after the UAE-based healthcare group said it would launch an independent review of its books, fell 7 percent. Its shares had nearly halved in value after short-selling firm Muddy Waters questioned its financials last week.
Telecom firm BT Group Plc (BT.L) was also among major blue-chip losers, giving up 2.2 percent.
Mid-cap gold miner Centamin Plc (CEY.L) added 1 percent, a day after it won an approval to give its Canadian suitor Endeavour Mining (EDV.TO) more time to make a firm takeover offer.
UK markets will shut early on Tuesday, and remain closed for Christmas and Boxing Day on Wednesday and Thursday, respectively.