-There is a slight chance that power cuts could occur and other services to some homes and businesses could be lost.
However, temperatures are still expected to be relatively warm in Lancashire, with peak temperatures of around 22C on Saturday and 20C on Sunday.
"With hot air over the United Kingdom some scattered thunderstorms may form over parts of central and eastern England on Thursday afternoon", said the Met Office.
The company tweeted that "unprecedented high temperatures" were "affecting the operation of air conditioning on our shuttles".
Fire brigades also called for a ban on BBQs in parks and drivers were urged not to throw rubbish following a string of grassland fires in recent weeks. The TUC has been campaigning for a change in the law to introduce a new maximum indoor temperature of 30C, or 27C for those doing strenuous jobs.
Northern Ireland, Scotland and Wales saw high temperatures of 26.2-29.4C.
Imran Khan ahead in Pakistan election polls amid rigging complaints
Bhutto - son of slain prime minister Benazir Bhutto - and his PPP could be called upon to form a coalition with any victor . The military, which has ruled Pakistan for almost half of its 71-year history, denies any effort to influence the election.
The Met Office has issued a yellow warning for torrential rain for eastern areas, and said there could be lightning, large hail stones and localised flooding.
Torrential downpours are possible, with as much as 30mm of rainfall in one hour and 60mm in three hours, while large hail, frequent lightning and strong, gusty winds will be additional hazards, forecasters warned.
A sweltering 37C (98.6F) is forecast for the South East and East Anglia, with the storms returning in the mid-afternoon and evening as the heat builds.
But the wet weather and cooler temperatures will just be a temporary respite as the mercury will likely rise again.
Meanwhile sun worshippers in the United Kingdom have sizzled in the hottest temperature of the year so far, with a scorching 33.3C recorded in England yesterday.