Sharecast - The FTSE 100 was flat at 7,749.83, having opened slightly lower.
Russ Mould, investment director at AJ Bell, said: "The FTSE 100 started Wednesday on the back foot as whispers in Washington about an impasse in debt ceiling talks soured the market mood.
"The first ever default on US debt is unthinkable and the likeliest outcome is an eleventh-hour deal but, as the beginning of June deadline for raising the debt ceiling signalled by US Secretary of the Treasury Janet Yellen draws closer, nervousness is likely to build.
"The extremely partisan nature of US politics is an obstacle to a deal as both parties seek to use the threat of the cliff-edge to secure concessions from the other side."
In equity markets, JD Sports Fashion PLC (LON:JD) was weaker even as it said it expects annual profit to pass £1bn after a record result in the year to January 28.
British Land Company PLC (LON:BLND) slumped after it said the value of its portfolio declined 12.3% in the year to the end of March as higher interest rates had an impact on property yields.
Credit-checking firm Experian PLC (LON:EXPN) was under the cosh after it reported a 19% drop in full-year pre-tax profit.
London Stock Exchange Group (LON:LSEG) fell after a consortium including Blackstone (NYSE:BX) and Thomson Reuters sold 33m shares in the company in a placing.
Watches of Switzerland tumbled as it hailed a "strong" full-year performance in line with guidance and reported record revenues and profitability, but warned of an expected sales decline in the first quarter.
Estate agent Savills (LON:SVS) slid as it said the first half will be "materially impacted" by the ongoing "recalibration of global investment markets".
On the upside, software firm Sage rallied after posting well-received first-half results and upgrading its outlook for full-year recurring revenue growth.
Auction Technology, Mitchells & Butlers and Keller were also up after results.
Online fashion retailer Asos surged after Mike Ashley's Frasers Group upped its voting rights to 7.4% from 5.1%.
Market Movers
FTSE 100 (UKX) 7,749.83 -0.02%
FTSE 250 (MCX) 19,184.17 -0.46%
techMARK (TASX) 4,718.77 0.10%
FTSE 100 - Risers
Sage Group (LON:SGE) 850.00p 3.53%
Rolls-Royce Holdings (LON:RR.) 151.00p 1.92%
Rio Tinto (LON:RIO) 4,974.00p 1.17%
BP (LON:BP.) 481.50p 1.17%
International Consolidated Airlines Group (LON:ICAG) SA (CDI) (IAG) 157.50p 1.16%
DCC (CDI) (LON:DCC) 4,838.00p 1.11%
Standard Chartered (LON:STAN) 626.60p 1.10%
CRH (CDI) (LON:CRH) 3,960.00p 0.94%
Glencore (LON:GLEN) 435.95p 0.89%
Smith & Nephew (SN.) 1,310.50p 0.89%
FTSE 100 - Fallers
JD Sports Fashion (JD.) 160.00p -6.02%
British Land Company (BLND) 355.30p -5.98%
Croda International (CRDA) 6,394.00p -4.28%
London Stock Exchange Group (LSEG) 8,126.00p -4.08%
Experian (EXPN) 2,663.00p -2.81%
Imperial Brands (LON:IMB) 1,801.00p -2.07%
Land Securities Group (LAND (LON:LAND)) 621.60p -2.05%
Ocado Group (LON:OCDO) 406.60p -1.83%
Intertek Group (LON:ITRK) 4,033.00p -1.37%
United Utilities Group (UU.) 1,066.00p -1.20%
FTSE 250 - Risers
ASOS (LON:ASOS) (ASC) 422.80p 5.99%
Auction Technology Group (ATG) 705.00p 5.22%
Mitchells & Butlers (MAB) 203.00p 4.05%
Keller Group (LON:KLR) 650.00p 2.20%
Future (FUTR (LON:FUTR)) 1,054.00p 1.93%
UK Commercial Property Reit Limited (UKCM) 55.70p 1.46%
RIT Capital Partners (LON:RCP) 1,942.00p 1.36%
easyJet (LON:EZJ) 512.60p 1.34%
Morgan Advanced Materials (LON:MGAMM) (MGAM) 293.50p 1.21%
Wizz Air Holdings (LON:WIZZ) 3,116.00p 1.20%
FTSE 250 - Fallers
Watches of Switzerland Group (WOSG) 685.00p -7.49%
Savills (SVS) 885.00p -5.65%
Coats Group (LON:COA) 69.10p -5.34%
Capricorn Energy (LON:CNE) 194.18p -5.32%
Ninety One (N91) 163.80p -4.99%
Wood Group (John) (WG.) 133.40p -4.17%
International Distributions Services (IDS) 222.30p -4.02%
Syncona Limited NPV (SYNC) 149.00p -3.25%
Ferrexpo (LON:FXPO) 101.70p -3.05%
W.A.G Payment Solutions (WPS) 97.60p -2.89%