Last checked at 
* FTSE 100 down 0.1%, FTSE 250 down 0.2%
* Sterling, housebuilders rally on parliament suspension
ruling
* U.S.-China trade sentiment earlier supported market mood
* Metro Bank falls after ditching bond issue
(Adds news items, analyst comments, updates share prices)
By Shashwat Awasthi and Muvija M
Sept 24 (Reuters) - London's exporter-heavy FTSE 100 fell to
session lows on Tuesday as sterling firmed after the Supreme
Court ruled that Prime Minister Boris Johnson acted unlawfully
when he advised Queen Elizabeth to suspend parliament just weeks
before Brexit.
The ruling, a major setback to Johnson who has promised to
deliver Brexit on Oct. 31 with or without a divorce deal with
the European Union, led the main index to hand back
earlier gains and slide as much as 0.3%.
"Fundamentally, it's hard to see how this gets the UK and EU
any closer to a deal that will be approved by MPs, but it does
really deliver a massive blow to Boris Johnson," Markets.com
analyst Neil Wilson said.
Shares of companies that book a major chunk of their
earnings in dollars slid, with BAT and Imperial Brands
giving up more than 1% each, while the JP Morgan index
that follows UK-listed companies making their money abroad
also hit session lows.
The more domestically-focused FTSE 250 index cut
some losses but was still 0.2% lower, with most market
participants still unsure as to how the already chaotic Brexit
process would now play out.
"I think the downward move in the FTSE 250 is due more
political uncertainty, the chatter of a general election is
going the rounds, which has chipped away at equity market
sentiment," said CMC Markets analyst David Madden.
Banks with a larger exposure at home, including Barclays
and RBS moved lower, brought the earlier
rebound in financial stocks to a premature end.
"It's extremely difficult to say whether the ruling will be
a game changer or nothing more than a headline maker but it will
certainly ramp up the Brexit theatrics, just over five weeks
ahead of the end of October deadline," Oanda analysts said.
However, stocks considered most sensitive to any updates on
the domestic economy reacted positively to the ruling. Blue-chip
housebuilders Persimmon and Berkeley added more
than 1% each.
The mid-morning proceedings took the spotlight away from
good news overnight that the United States and China will resume
trade talks next month.
After its steepest monthly fall this year amid escalating
trade tensions and recession fears in August, the blue-chip
index has rebounded this month as various central banks have cut
interest rates to counteract slowing global growth.
Among a few notable news-driven movers was mid-cap A.G. Barr
which jumped 6% after the soft drinks maker stuck to its
annual forecast despite a "disappointing" first half.
Among smaller stocks, Metro Bank sank almost 17% to
a new life-low, as the troubled lender ditched a 250 million
pound bond issue on Monday after failing to attract investors.
"It shows the kind of mire Metro is in after the accounting
error and now expanding FCA investigation ... this is a worrying
sign that the bank is not able to raise fresh debt and/or
capital when the going gets tough," Wilson said.
AIM-listed ad agency M&C Saatchi slid 12% to its
lowest in more than seven years after warning annual profit
would fall 5%-10% below estimates.
(Reporting by Indranil Sarkar and Shashwat Awasthi in Bengaluru
and Josephine Mason in London; Editing by Bernard Orr and Ed
Osmond)
