The Queen has resumed her train journey to Tweedbank as she marks her historic day by inaugurating the new £294 million Scottish Borders Railway.
Prime Minister David Cameron has paid fulsome tribute to the Queen on the day she becomes Britain's longest running monarch, describing her reign as a "golden thread running through three post-war generations".
Speaking in the House of Commons, Mr Cameron said: "I do think it's right that today we should stop and take a moment as a nation to stop and mark this historic milestone."
Her Majesty the Queen inspires us all with her remarkable service, her dignified leadership and the extraordinary grace with which she carries out her duties.
It is truly humbling to comprehend the scale of service that Her Majesty the Queen has given this country. The reign of Queen Elizabeth II has been a golden thread running through three post-war generations.
The Queen is our Queen and we couldn't be more proud of her. She has served this country with unerring grace, dignity and decency. And long may she continue to do so.
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Queen Elizabeth will be arriving at Tweedbank Station at around 1:20pm today, and excitement is building.
We've been speaking to some of the people waiting patiently at the station:
We wanted to bring Ella to see the queen come to the Borders on the steam train."
I'm excited to see the queen coming and opening the railway. I like how she wears nice hat."
Trains coming back to Borders and it's an historical day for the Queen and it's great she's given her big day to us and the Borders.
I was the customer assistant at Tweedbank station and I used to look after the paperwork."
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The Queen is set to overtake her great-great-grandmother Queen Victoria as Britain's longest serving monarch.Read the full story ›
The Queen's train has left Waverley Station in Edinburgh.
She is now travelling down to the Scottish Borders to open the Borders Railway, and is expected to arrive at Tweedbank around an hour late, after fog delayed her helicopter.
Queen Elizabeth's visit to the Scottish Borders has been delayed by around an hour.
It's because the royal helicopter has been delayed at Balmoral Castle, in Aberdeenshire, by fog.
Howard Armstrong walked from Cummersdale to Carlisle, to see Queen Elizabeth on her visit in 1958.
He was eleven at the time, and went on to work on the Royal Train for the British Transport Police.
His fascination with the Royal Family continues today:
I'd gone into Woolworths to buy a Union flag to wave and it was fantastic because we saw right close up. Where I was standing was beside the fence, the barrier, and the royal car came right down, it was a glass backed car, and it was fantastic, a fabulous day.
I'm a fanatic royal. Well I'm saying that, I'm not, I don't go out of my way to see them, but if the Queen was to come back to Carlisle I'd be one of the first in the queue."
A crowd has gathered in the car park at Tweedbank Station, waiting for the Queen's arrival.
People have been queuing outside the station since around 6am this morning, and were allowed into the car park at 9am.
Queen Elizabeth is expected to arrive at the station at 12:18pm, where she will officially open the new Borders Railway.