The UK's main stock indexes closed lower for a third consecutive session on Thursday amid political uncertainty ahead of UK's elections in July, while news of slower growth across businesses in May weighed on sentiment.

The blue-chip FTSE 100 index and mid-cap FTSE 250 each tumbled 0.4%.

A surprise call for a general election by Prime Minister Rishi Sunak spooked investors as they weighed the potential scenarios.

"Markets like certainty, and pre-election there is caution and a sort of political uncertainty that could weigh on demand for UK stocks and the pound," said Fiona Cincotta, senior market analyst at City Index.

Utilities shares fell 7.1%, leading declines among sectors, after energy infrastructure operator National Grid said it is looking to sell its Grain liquefied natural gas (LNG) terminal in Britain. The stock fell 10.9%, the biggest loss on the FTSE 100.

Precious metal miners weighed on the markers with a 1.7% slide, tracking lower prices of gold and silver.

On the brigher side, aerospace and defence sector gained 2.4%, boosted by Qinetiq Group after it hit a record high on an upgraded financial year outlook.

An upbeat quarterly earnings report from American chipmaker Nvidia boosted technology shares across global markets, lifting the U.S. benchmark S&P 500 and tech-heavy Nasdaq hit record highs.

A survey showed growth across British businesses had cooled more than any economist polled by Reuters had predicted.

Among stocks, Hargreaves Lansdown surged 14.4% after the investment platform rejected a 4.67 billion pound ($5.94 billion) takeover proposal.

Gains in Hargreaves supported the investment banking sector to a more than two-year high.

(Reporting by Pranav Kashyap and Purvi Agarwal in Bengaluru; Editing by Sohini Goswami, Krishna Chandra Eluri and Richard Chang)