Sharecast - At 0830 BST, the FTSE 100 was down 0.2% at 7,734.44.
Susannah Streeter, head of money and markets at Hargreaves Lansdown (LON:HRGV), said: "Investors are staying cautious as talks aimed at averting a US default continue, with US Treasury Secretary warning that deep cracks in the financial system would appear if budget agreement is not reached.
"However, there is a small sliver of more optimism with the Republican Speaker of the House of Representatives, Kevin McCarthy, saying that progress can be made by the end of the week."
In equity markets, credit-checking firm Experian 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.
British Land slumped after it said the value of its portfolio declined by 12.3% in the year to the end of March as higher interest rates had an impact on property yields.
JD Sports Fashion was in the red even as it said it expects annual profit to pass £1bn after a record result in the year to January 28.
Watches of Switzerland tumbled as it hailed a "strong" full-year performance in line with guidance, with record revenues and profitability, but warned of an expected sales decline in the first quarter.
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 and Bank of Georgia were also up after results.
Market Movers
FTSE 100 (UKX) 7,734.44 -0.21%
FTSE 250 (MCX) 19,197.57 -0.39%
techMARK (TASX) 4,721.19 0.15%
FTSE 100 - Risers
Sage Group (LON:SGE) 841.80p 2.53%
Rolls-Royce Holdings (LON:RR.) 150.65p 1.69%
Vodafone Group (LON:VOD) 84.39p 1.27%
DCC (CDI) (LON:DCC) 4,829.00p 0.92%
AstraZeneca (NASDAQ:AZN) 12,152.00p 0.68%
Smurfit Kappa Group (CDI) (SKG) 3,014.00p 0.67%
Antofagasta (LON:ANTO) 1,413.00p 0.64%
Pershing Square (NYSE:SQ) Holdings Ltd NPV (PSH) 2,718.00p 0.59%
Convatec Group (CTEC (LON:CTEC)) 219.20p 0.55%
Rio Tinto (LON:RIO) 4,943.50p 0.55%
FTSE 100 - Fallers
Experian (EXPN) 2,584.00p -5.69%
London Stock Exchange Group (LSEG) 8,110.00p -4.27%
British Land Company (BLND) 365.40p -3.31%
JD Sports Fashion (JD.) 166.55p -2.17%
Croda International (CRDA) 6,550.00p -1.95%
Ocado Group (LON:OCDO) 406.60p -1.83%
Land Securities Group (LAND (LON:LAND)) 626.40p -1.29%
Kingfisher (LON:KGF) 239.40p -1.20%
Imperial Brands (LON:IMB) 1,817.00p -1.20%
Endeavour Mining (EDV (LON:EDV)) 2,020.00p -1.17%
FTSE 250 - Risers
Auction Technology Group (ATG) 712.00p 6.27%
Bank of Georgia Group (BGEO) 3,485.00p 3.26%
Jupiter Fund Management (JUP) 121.30p 2.28%
Pets at Home Group (PETS) 395.00p 1.59%
ASOS (LON:ASOS) (ASC) 405.20p 1.58%
Petershill Partners (PHLL) 148.80p 1.50%
Domino's Pizza Group (DOM) 300.00p 1.49%
Spire Healthcare Group (SPI) 243.00p 1.46%
FirstGroup (FGP (LON:FGP)) 118.50p 1.11%
Genuit Group (GEN) 307.00p 0.99%
FTSE 250 - Fallers
Watches of Switzerland Group (WOSG) 658.50p -11.07%
Ninety One (N91) 166.90p -3.19%
IWG (IWG) 146.40p -2.66%
Safestore Holdings (SAFE) 940.00p -2.34%
Bridgepoint Group (Reg S) (BPT) 217.00p -2.16%
Tullow Oil (LON:TLW) 22.12p -2.12%
Assura (AGR) 51.50p -2.09%
IntegraFin Holding (IHP) 273.00p -2.01%
Chemring Group (CHG (LON:CHG)) 276.00p -1.95%
Savills (LON:SVS) 920.00p -1.92%