Foreign Secretary William Hague is committing an additional £5m to fund communications equipment and medical supplies - mostly to the largest rebel group, the Free Syrian Army (FSA).
Comment: Yeh, that's "communications and medical supplies" in inverted commas, like how the Scott Inquiry confirmed that the UK government was brokering contracts with Saddam Hussein in the late 1980s to sell him "farming equipment."
However, the assistance will not include any weapons.
The BBC's James Robbins says the move is a significant shift in policy after months of British frustration about divisions within Syria's opposition.
There have also been complaints that the opposition has failed to set out a clear programme for good government, our correspondent added.
Attempts to oust President Bashar al-Assad have led to 17 months of unrest, during which activists claim more than 20,000 people have died.
However, reports of casualties often cannot be independently verified.
The UK is also telling opposition forces they must observe human rights standards.
The extra practical support for the opposition FSA will include more radio and satellite equipment, as well as portable power generators.
The Foreign Office says it will help protect activists from repression and help them overcome the Syrian government's jamming and blocking techniques.
It said Britain has previously made £1.4m available in "non-lethal support to the political opposition". This has included providing training and assistance to human rights groups in Syria.
Funding totalling £27.5m is also being provided by Britain for humanitarian aid such as food, medical care and shelter in Syria, as well as for Syrian refugees who have fled to neighbouring countries. Some 800 of these also need assistance with water sanitation.
Comment: Humanitarian aid, right. And who is going to make sure this aid gets to those who need it? Al-Qaeda-in-Syria aka the Syrian Rebels (sic)? The same barbarians running around cutting off children's limbs, posting video footage of their deeds on YouTube, then pinning it on Assad's forces?
German intelligence working to bring 'al Qaeda' barbarians to power in Syria
International Development Secretary Andrew Mitchell had announced last week that the amount of assistance being given to the refugees was being quadrupled by a further donation of £10m.
This support follows on from the assistance given by Britain to Libya during the uprising against Colonel Gaddafi last year. This included supplying shelter for both refugees and those made homeless, supporting mine clearance and also helping the World Health Organization to provide medical care.
Mr Hague, writing in the Times, says it remains British policy not to send arms to Syria, and also describes the Assad regime as "doomed".
He added: "It has turned Syria into a magnet for men of violence, from the regime's men of violence to terrorists slipping across the borders.
"This is not taking sides in a civil war. The risk of total disorder and a power vacuum is so great that we must build relationships now with those who may govern Syria in the future."
And he says the risk of not working with Syrians who want a democratic and open Syria is that the conflict will be hijacked by al-Qaeda and other extremists.