Dec 31 unless Congress intervenes.
"U.S. lawmakers have this week left to dig in their heels and flesh out a deal otherwise it is unlikely the FTSE 100 will be sitting above that 5,900 level by the end of the year," Ishaq Siddiqi, market strategist at ETX Capital said.
Strength in miners helped limit the blue chip falls, adding over 8 points to the index, with the sector supported by improving data from top metals consumer China, following a year of underperformance which has seen the sector fall 1.6 percent compared with the FTSE 100's 6.3 percent rise.
"Materials is the only cyclical sector to have underperformed so far in 2012 and hence could be a key beneficiary of the 'January' effect in 2013," they add, reiterating a preference for mining, and pointing to a recent trend where the worst performers of the prior year have triumphed in January.
Airlines owner IAG was the top FTSE 100 gainer, up 3.3 percent in strong volume of 140 percent of its 90-day daily average, after its Spanish unit Iberia said it had agreed to negotiate with its unions over a five-year restructuring plan to ensure the airline's future viability.