The Three Million group, a pressure group comprising of EU nationals living in the UK, are seeking a guarantee from the government that they can remain in the country after Britain exits the European Union. They are also seeking permanent residence status before Article 50 is triggered.

The group, together with 10 others that represent the 1.2 million British citizens living in the EU, plan to present a letter listing their demands to Downing Street.

"We are not bargaining chips. We are people," the letter states. Around 2.8 million EU nationals live in the UK, the BBC says.

UK government says status of EU nationals depends on member states

Prime Minister Theresa May has been quite clear on her stance over EU nationals living in the UK. She has said that although the government wants to protect EU nationals, EU member states also need to reciprocate and protect British citizens.

The UK and EU flag Adam Berry/ Getty Images

She has insisted that the government will not simply "give away the guarantee for rights of EU citizens here in the UK" without guaranteeing the rights of UK citizens in EU member states.

A statement from the government said that although it wanted to guarantee the future residence for EU nationals already living in the UK, this depended on the 27 member states, BBC reports.

"The Prime Minister and other ministers have been absolutely clear that they want to protect the status of EU nationals already living here. The only circumstances in which they wouldn't be possible is if British citizens' rights in European member states were not protected in return."

UK should make first move to demonstrate goodwill

Theresa May
Britain's Prime Minister Theresa May Carl Court/ Reuters

Think tank British Future has called for the current EU permanent residence system to be converted into the "indefinite leave to remain" status which is in place for other international migrants living in the UK.

It said that the "complex and expensive process" should be streamlined and costs capped.

The British Future report said that it was "morally wrong to use EEA+ [EU and Norway, Iceland, Liechtenstein and Switzerland] nationals in the UK as bargaining chips to secure the rights of UK nationals in Europe."

MP Gisela Stuart, who headed the Vote Leave campaign during the EU referendum and the chair for the think tank panel, said: "Britain should make clear at the start of the Brexit negotiations that EU citizens already here before that date can stay."

"This would send a clear signal about the kind of country the UK will be after Brexit and the relationship we want with Europe. We should expect reciprocal deals for Britons living in European countries, but Britain should make the first move to demonstrate goodwill," she added.