Frank Mugisha does not know whether he will be arrested on return to Kampala. If the antihomosexuality Bill becomes law, the chief executive of Uganda's main gay rights group could face life imprisonment.
The outcome is likely to depend on medical advice.
Uganda's President Yoweri Museveni, who will decide in the coming days whether or not to sign the legislation into law, has commissioned reports from doctors and geneticists.
He says he can only give his assent if scientists prove that homosexuals are made, not born.
Museveni's delay, or reluctance, in giving presidential approval is also due to an expectation that there will be a furore of disapproval from international donor nations and business investors.
Last month the US secretary of state, John Kerry, publicly condemned Nigeria for introducing a similar law, the Same Sex Marriage Prohibition Act.
Mugisha (32) runs Sexual Minorities Uganda (Smug), a semi-clandestine network that dares not advertise its presence and is regularly forced to move office for fear of attack.
One of his former colleagues, David Kato, was murdered in 2011.
Uganda already has so-called sodomy laws, inherited from the British colonial era, that criminalise same-sex acts.
"People get arrested but no one has ever been convicted.
It's difficult to enforce," explained Mugisha, who is in London to brief human rights groups and talk to the Foreign Office about the new legal threat.
Two Britons have been deported from Uganda in the past year after being charged under existing laws with allegedly possessing a gay sex video and staging a play about gay people.
Neither were convicted.
The new antihomosexuality Bill extends the punishments available to life imprisonment and creates additional crimes, with up to seven years in jail, for those convicted of advocating or supporting gay rights.
"I'm openly gay," said Mugisha.
"I could be arrested. This Bill criminalises all gay groups and any debate about the issue.
"Already ordinary Ugandans are acting as though the law has been passed. People are calling the police [with names of suspects] and harassing others in the streets. If this Bill is passed we are going to see many other African countries coming up with similar laws."
Mugisha, who was brought up in Kampala, blames not only the British legal heritage but also American evangelists who have arrived in sub-Saharan Africa to preach against homosexuality and promote a new wave of anti-gay legislation.
Fight for survival
Smug has consequently been forced to pursue its legal fight for survival as far afield as Massachusetts, where it is suing one evangelist, Scott Lively, for crimes against humanity and persecuting gay groups in Uganda contrary to US law.
Lively has claimed his words were taken out of context and that the claim is absurd and frivolous.
"People [condemning homosexuality] talk about 'African values' but don't think what that actually is," said Mugisha.
"Male Africans are very defensive about sexuality. They think talking about it undermines their sexuality. There's fear and confusion about the unknown."
Mugisha and his network of 18 lesbian and gay organisations have produced their own report for Museveni.
"It shows that homosexuals are born gay and that homosexuality is not alien to Africa," Mugisha said.
The president's ruling National Resistance Movement (NRM) party has gone into a 10-day retreat outside the capital, Kampala.
Museveni is expected to announce whether the Bill will be signed into law before the retreat ends on February 16.
One of those who drew up a medical report for the president, Dr Kenneth Omona, told Uganda's Observer newspaper: "One study revealed that actually 50% of the homosexuals revert to heterosexuality if rehabilitated in time. This, in itself, reveals a behavioural aspect."
Mugisha wants to stiffen the resolve of nations, such as the UK, that provide aid and support.
"Don't cut aid, don't tell the [Ugandan] government what to do but have a proper dialogue.
We don't want multinationals to leave Uganda.
If Coca Cola leaves or KLM doesn't fly in any more, it's Ugandans who will suffer," he said.
"But if the Bill is passed, there could be consequences. A lot of people will feel ashamed to invest in Uganda. People should be saying strong words now, not saving them for when the Bill is passed."
Mugisha added: "I'm not scared of Ugandan politicians. I will stand my ground. I have experienced violence myself many times in the past. I live an openly gay life but have to be careful."
Jonathan Cooper, chief executive of the London-based Human Dignity Trust that campaigns to decriminalise homosexuality around the world and has supported Mugisha, said: "The next few days are absolutely crucial.
The international community now has a very narrow window within which to stand in solidarity with Frank and the Ugandan LGBT community and call for Museveni to put a stop to this cruel piece of legislation.
"Not only will the proposed antihomosexuality law persecute many ordinary Ugandans, leading to violence, it breaches the country's own constitution and international human rights law."
The British Foreign and Commonwealth Office (FCO) spokesperson said: "We're concerned about the potential impact on human rights in Uganda of the antihomosexuality Bill, which would increase further the existing sanctions against homosexuality.
"It is wrong that LGBT individuals continue to suffer persecution, violence, and intimidation.
We expect Uganda to live up to the values where all its citizens are free to live their lives in a safe and just society."
The minister for Africa, Mark Simmonds, the FCO added, raised the issue with his Ugandan counterpart on two occasions in December last year and again last month. – guardian.co.uk © Guardian News and Media 2014