Queen Elizabeth inspects London's new Elizabeth line

Queen Elizabeth II and Prince Edward arrive at Paddington station in London to mark the completion of London's Crossrail project and to view the new Elizabeth Line. PA

Queen Elizabeth using a oyster card machine at Paddington station. PA

The queen meets staff who have been key to the Crossrail project, as well as Elizabeth Line staff who will be running the railway. PA

The queen and Prince Edward unveil a plaque at Paddington station. PA

Prince Edward and Howard Smith, chief operating officer of Elizabeth Line, board one of the line's trains. PA

Prince Edward talks to driver Carinne Spinola in the cab of an Elizabeth Line train. PA

British Prime Minister Boris Johnson with Transport Secretary Grant Shapps, centre right, and Mayor of London Sadiq Khan, centre left, on an Elizabeth Line train at Paddington station. PA

Boris Johnson in the driver's seat of a train. PA

"We're all incredibly touched and moved and grateful to her Majesty for coming to open the Elizabeth line today. It was fantastic to see her," Prime Minsiter Boris Johnson said. PA

Boris Johnson speaks with staff at the station. PA

Britain's Queen Elizabeth II has made a surprise appearance at London’s Paddington station to inspect the new multibillion pound Elizabeth Line, named in her honour.

The queen was accompanied by her youngest son, Edward, Earl of Wessex, for the official visit on Tuesday, as the line gears up for its official opening later this month.

Only two weeks away from her platinum jubilee celebration, she now rarely carries out public engagements because she walks with difficulty.

“In a happy development, her majesty the queen is attending today's event to mark the completion of the Elizabeth line,” a Buckingham Palace spokeswoman said.

“Her Majesty was aware of the engagement and the organisers were informed of the possibility she may attend.”

Her attendance was not announced in advance, because of the mobility concerns.

Tuesday's engagement was the queen's first outside the Windsor, area since she attended the Duke of Edinburgh's memorial service at Westminster Abbey seven weeks ago.

She took a return trip to Tottenham Court Road, and met train drivers, station staff and apprentices.

The Earl of Wessex said: "That was brilliant. I did enjoy that. It was good fun."

The queen and Prince Edward were welcomed by Prime Minister Boris Johnson, Mayor of London Sadiq Khan and Transport for London commissioner Andy Byford.

"We're all incredibly touched and moved and grateful to her Majesty for coming to open the Elizabeth line today. It was fantastic to see her," Mr Johnson said,

The Elizabeth line will open to passengers on May 24.

Crossrail, the project to build the new east-west railway, was delayed and ran over budget because of numerous issues including construction difficulties and complications while installing signalling systems.

It was due to be completed in December 2018, with a budget of £14.8 billion set in 2010.

The total cost has been estimated at £18.9 billion, including £5.1 billion from the government.

The Elizabeth line will boost capacity and cut journey times for travel across the capital.

It will stretch from Reading, in Berkshire, and Heathrow Airport, in west London, to Shenfield, in Essex, and Abbey Wood, in south-east London.

Trains will initially operate in three sections, which are expected to be integrated in the autumn.