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By Paul Sandle and William Schomberg
LONDON, Nov 8 (Reuters) - Moody's warned on Friday it might cut its rating on Britain's sovereign debt again, saying that neither of the main political parties in next month's election was likely to tackle high borrowing levels which Brexit had made even harder to fix.
In a toughly worded statement, Moody's said the fissures in Britain's society and politics exposed by its still-unresolved decision to leave the European Union would be long-lasting.
"It would be optimistic to assume that the previously cohesive, predictable approach to legislation and policymaking in the UK will return once Brexit is no longer a contentious issue, however that is achieved," the ratings agency said.
Moody's said Britain's 1.8 trillion pounds ($2.30 trillion) of public debt - more than 80% of annual economic output - risked rising again and the economy could be "more susceptible to shocks than previously assumed."
Both of the main political parties have promised big spending increases ahead of next month's election.
"In the current political climate, Moody's sees no meaningful pressure for debt-reducing fiscal policies," the ratings agency said.
Prime Minister Boris Johnson called the Dec. 12 election in an attempt to break the deadlock over how, and even if, the country should leave the EU, more than three years after the Brexit referendum.
Moody's said the "increasing inertia and, at times, paralysis that has characterized the Brexit-era policymaking process" showed how the UK's institutional framework has diminished.
Even once Britain was out of the EU, uncertainty would remain because of the "significant challenges" of reaching a future trade deal with the bloc, it said.
Any signs that Britain was unable to replicate the benefits of EU membership with trade deals in Europe and beyond would also be negative for the rating.
Moody's, which stripped the country of its AAA rating in 2013 and downgraded it again in 2017, said it was lowering the outlook on Britain's current Aa2 rating to negative from stable, meaning the rating could be cut again.
At Aa2, Britain is on the same level as France but below Germany's AAA rating by Moody's.
Moody's said the government, after reducing a budget deficit which leapt to 10% of GDP in 2010, had been increasingly willing to "move the goalposts" on making further progress.
"Successive governments have announced large, permanent increases in public expenditures, most notably a large increase in spending on the National Health Service, outside the normal calendar for fiscal policy changes and without detailed policy plans," it said.
Last month, ratings agency Standard & Poor's said it would cut Britain's AA credit rating if the country leaves the EU without a deal, and it, too, warned that Brexit indecision was causing government paralysis.
($1 = 0.7832 pounds) (Reporting by Paul Sandle and William Schomberg Editing by Bill Berkrot and Leslie Adler)