FILE PHOTO: The Fitch Ratings logo is seen at their offices at Canary Wharf financial district in London,Britain, March 3, 2016. REUTERS/Reinhard Krause

LONDON (Reuters) - Ratings agency Fitch said on Friday it no longer assumed that Britain would leave the European Union in a smooth transition and said an acrimonious and disruptive “no deal” Brexit could lead to a further downgrade of its sovereign credit rating.

“In Fitch’s view, an intensification of political divisions within the UK ... has increased the likelihood of an acrimonious and disruptive ‘no deal’ Brexit.

“Such an outcome would substantially disrupt customs, trade and economic activity, and has led Fitch to abandon its base case on which the ratings were previously predicated.”

Previously Fitch had assumed Britain would leave the EU in March next year with a transition deal in place and the outline of a future trade deal with the bloc.

But Prime Minister Theresa May has struggled to agree a deal that can secure the backing of Brussels and her own lawmakers in the Conservative Party.

The ratings agency currently rates British government debt at AA with a negative outlook which means a further lowering of the rating is possible. Fitch cut its top-notch AAA rating on Britain in 2013, citing the outlook for weaker public finances.

Ratings downgrades up to now have had little impact on investors’ appetite for British government debt, which is still seen as a safe asset at times of political or economic turmoil.

But downgrades are embarrassing for May’s Conservative government, which emphasised preserving the country’s AAA rating when it embarked on an austerity programme in 2010.