London mayoral election: Why will the result not be announced today?

Londoners will likely have to wait until late on Saturday to learn whether Sadiq Khan or Susan Hall has won the mayoral contest.

Some two million Londoners were expected to take part in the poll.

The timetable saw polling stations close at 10pm on Thursday.

So some people, eagerly watching to find out who has won, will be asking why does it take this length of time to announce a result.

After voting ended, the ballot boxes had to be secured from the more than 3,600 polling stations across the capital, staffed by some 12,000 people.

They were then securely transported to 14 counting centres in the city, which was expected to take until midnight.

The boxes were set to be secured overnight at the centres before verification starts at 9am on Friday.

Many of the election staff volunteer for this role, including a sizeable number from councils.

While they may get a small payment for this work, many of them will take part in several stages of the electoral process.

Thousands of staff will take part in the verification and counting of votes.

The verification process is to ensure that the number of votes received is correct as recorded being issued by polling station staff.

Any significant discrepancy could spark inquiries about missing votes.

Previous mayoral elections have used machines to e-count the votes under the old system where people could declare a first choice and second preference for mayor.

The votes are being counted manually this year as there was a possibility that a general election could also have been held on May 2, which would have had to be counted manually, and having two counting systems would have delayed results.

The first-past-the-post voting system is also being used for the first time for the London mayoral contest.

Estimates have suggested that if manual voting had been used in the previous mayoral elections, using the old voting system, then it could have take three days to get to the final result.

But using first-past-the-post should significantly speed up the count.

The count will start at 9am on Saturday.

Three separate ballot papers will needed to be counted.

The mayoral votes will be counted first, then the constituency London Assembly members, and finally the London-wide Assembly members who will be elected using the Modified d’Hondt proportional representation system.

The first results on the mayoralty may come in around midday on Saturday, with speculation that by around 1.30pm it might be clear who will emerge as the winner.

But as this is the first time that the first-past-the-post system is being used, and the votes are being counted manually, the results may come in far later.

When they do, the results will be sent to City Hall to be collated before the winner is formally announced.

Using e-counting is quicker but there have been concerns that such a method could be at risked of being hacked.

A manual count is more old-fashioned but it may reassure some Londoners that there has been no interference in the electoral system.