UK stocks edged lower on Tuesday as political uncertainty surrounding Prime Minister Keir Starmer's future unsettled investors, while concerns over renewed Middle East conflicts heightened market anxiety over inflation.

Despite Starmer's earnest appeal on Monday urging voters and Labour MPs to support his continued leadership and avoid a party leadership contest—warning that internal party strife would lead to chaos—market doubts about the UK's domestic political stability persisted.

Starmer has vowed to remain in office, yet his position appears increasingly precarious. More than 80 Labour MPs have publicly called for him to set a resignation timeline to facilitate an orderly transition to a new party leader.

Neil Wilson, UK investment strategist at Saxo Bank, noted, "Markets have always disliked uncertainty over the government's leadership," highlighting the UK's already fragile fiscal position.

As of 11:52 GMT, the UK's FTSE 100 blue-chip index fell 0.4%, while the mid-cap FTSE 250 index dropped sharply by 1.1%.

Driven by market concerns, the UK's long-term borrowing costs surged to near 30-year highs. Investors worry that if Starmer steps down, his successor might adopt more left-leaning policies favoring increased fiscal spending, a move that could strain the UK's already tight finances.

David Morrison, senior market analyst at Trade Nation, commented, "Overall market sentiment is very tense, and investors are deeply confused, wondering: What exactly is Starmer doing?"

Investors are also concerned about the slow progress in resolving Middle East conflicts, with U.S. President Donald Trump describing the ceasefire agreement with Iran as "barely hanging by a thread."

Tehran has rejected the U.S. proposal to end the conflict, insisting on a series of demands that Trump dismissed as "nonsense."

Oil prices jumped in response, with Brent crude futures rising 3%, further exacerbating concerns about the financial burden on UK households.

Banking stocks fell 2.6%, led by a 5.2% drop in Metro Bank shares and a 4.0% decline in Barclays, dragging the sector lower.

Aerospace and defense stocks also slipped 1.9%, while interest rate-sensitive real estate shares declined 2.1%.