Gary McKinnon, the London-based computer hacker who won a decade-long battle against extradition to the US in 2012, has been cautioned by his lawyers against visiting Scotland because he may still be extradited from there.

McKinnon wants to visit his seriously ill father in Glasgow but has been told that, because Scotland has a different legal system to England, the US authorities could make a fresh bid to extradite him once he was there.

McKinnon, working out of his bedroom in north London, hacked into the computer systems of Nasa and the US defence department in search of information about UFOs nearly fifteen years ago.

The US launched a bid to extradite him to stand trial but, after a series of legal actions, home secretary Theresa May ruled in his favour on the grounds that his extradition "would give rise to such a high risk of him ending his life that a decision to extradite would be incompatible with Mr McKinnon's human rights."

Now McKinnon wants to visit his father, Charlie, who is in hospital having suffered a stroke.

"His legal team have advised him that, because May's decision applies only in England and Wales, the US could attempt to extradite him," says Janis Sharp, McKinnon's mother, who led the fight to keep her son from being extradited.

"Gary is extremely upset as he wants to visit his dad but is afraid because of the advice not to go there. Couldn't the Scottish government just say that they'll abide by Theresa May's decision?"

A Scottish government spokeswoman said: "while we do not comment on individual cases, there is no reason to suppose that anyone for whom extradition was refused in the rest of the UK would necessarily see it granted in Scotland.

Scottish Ministers also have no power to act in contravention of the European Convention on Human Rights."

With the Scottish independence vote now only weeks away, the issue has other ramifications: would an independent Scotland feel committed to past legal decisions made by UK government ministers?

A spokesperson for the Law Society of Scotland said that they did not comment on individual cases but pointed out that the Extradition Act of 2003, which embodies the UK-US extradition treaty, applies to the whole of the UK and that – at least for the immediate future – includes Scotland.

Following independence, existing laws, whether passed by the Westminster or Scottish parliament, would continue to apply until or unless they were amended by the independent Scottish parliament.

McKinnon has rebuilt his life after being allowed to use computers again – one of his bail conditions banned him from doing so.

He has started a small business, Small SEO, which uses his technical computer skills. There are also plans to turn his story into a film.

• This article was amended on 1 August 2014 because an earlier version said the Scottish independence vote was weeks ago, when weeks away was meant.