The 83-year-old Harry Potter star has been dating Heather Sutherland, 81, since they met while working on a BBC radio drama together in the late 1960s but they have always lived apart.
The couple own a house together in Italy and have decided they finally want to take the plunge and live together but MiriamMargolyes fears Britain's exit from the European Union has ruined their plans.
"We want to live together now because we haven't got long left," she told SAGA magazine.
"She is 81 and I am 83 - we don't know yet how we are going to do that.
"Brexit ruined our life when it comes to living in Italy, so it really is a problem."
Margolyes was full of praise for her partner.
"My life is made whole by the fact that she is in it," she said.
"Heather is magnificent, highly educated, an academic and very private."
Margolyes and Sutherland own a house in Tuscany and the actress previously revealed she planned to retire to the Italian countryside.
"I love travelling and meeting people and Italy is one of the countries of my heart," Margolyes said during an episode of the Loose Ends podcast for BBC Radio 4.
"I want to retire there with Heather.
"I've got a home in Clapham and I've had that since '73.
"I feel at home wherever I am and I always bought houses because I had the money to, because I didn't have children.
"If you have children, you're poor.
"You're rich in happiness I suppose."
The actor also previously revealed the secret to the couple's long-running relationship was the fact that they lived apart even after they entered into a civil partnership together.
"We were able to lead our lives without diminishing them," Margolyes told British Vogue magazine.
"I didn't want her to have to give up anything and I didn't want to give up anything.
"I wanted my cake and I wanted to eat it too and so far, it's worked."
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