UK government debt could be downgraded by DBRS Morningstar, according to a notice from the credit rating agency issued within the past 24 hours - even before the shock announcement that the UK would get its third prime minister of the year..

The credit arm of Morningstar said the debt was "under review with negative implications."

The reasons are clear: ongoing concerns about UK fiscal and other policies, alongside turmoil in the market for UK government debt.

DBRS Morningstar rates UK government debt as 'AA (high)', which is not far off 'AAA'. But this could be downgraded if it spots evidence of lasting negative impact, such as to the credibility of the government's fiscal plans.

Alternatively, the rating could be maintained if a credit plan is put forward regarding the longer term management of debt.

This is the latest in a string of credit warnings issued by rating agencies in the wake of the disastrous Mini-Budget of last September, which saw a huge spike in the cost of borrowing to fund UK government expenditure.

Fitch announced an 'Outlook Negative' on 5 October, stating that: "The large and unfunded fiscal package announced as part of the new government's growth plan could lead to a significant increase in fiscal deficits over the medium term."

Of particular interest in regards to the additional uncertainty another political leadership contest now brings to considerations of UK sovereign debt, Fitch added that the lack of an independent evaluation of the Mini-Budget measures in September had "negatively impacted financial markets' confidence and the credibility of the policy framework, a key long-standing rating strength."

The UK 10-year gilt was trading at around 3.87 towards the end of the session today, as the initial market welcome to Lis Truss' resignation announcement wore off.