Ivon Sampson, head of immigration at London law firm Healys LLP, said the UK is not showing enough support to the three million residents from other member states.
A help line would allay the fears many now have over loss of residency status, whatever future relationship is negotiated between the UK and the EU.
Mr Sampson said: “It would be the action of a decent country not seeking to add to the stress many who live, work and contribute to our society must now be feeling.”
He said their position was not as bad as it may appear post Brexit.
“Anyone who has been exercising EU treaty rights (for example; as a worker or as a student) for five years from another member state may have an right to settlement in the UK. It does not require them to take out UK citizenship, which would limit the amount of time they could spend abroad each year.
“In addition, the Vienna Convention  which governs the laws of international treaties , to which the UK is a signatory, protects the acquired rights of individuals in situations of treaty change.
Mr Sampson said there had been some “hysteria” over what may happen to EU residents living here in future with the UK outside the EU.
“I have taken calls from many EU nationals living and working in the UK who worried about their future position. I tell them not to be alarmed. It is very unlikely that rights to remain in the UK can be taken away from those who are already here. Indeed, they can generally secure their position further, and easily, by applying for settlement. The same rights also extend to students who are here.”
He added that the Vienna Convention principles would apply across Europe. “I cannot foresee a situation where, say, the Spanish government could ever withdraw rights and protection to UK citizens living in their country now, or moving there whilst we are still members of the EU.”