Mugabe, who is running for a sixth term in office, dismissed the main opposition party, the Movement for Democratic Change (MDC), saying they were supporting British interests.
"You in the MDC, it's treasonous to continue assisting the British to make sure they have a say here," he said.
The opposition denies any direct links with Britain.
British companies threatened
Mugabe warned the UK to stay out of Zimbabwean politics if it wanted to safeguard the interests of British companies working in the former colony.
"They still have companies which are still here and we did nothing to them ... 400 British companies and so they must take care," he said.
Britain and other countries have criticised Mugabe for violating political and human rights in his country and leading it into a disastrous economic crisis.
The UK says only 40 British firms remain operating in the country.
Both unemployment and poverty rates in Zimbabwe hover above 80 per cent and at least a quarter of the population has fled misery to seek economic refuge elsewhere.
Mugabe made no mention of Simba Makoni, who has broken ranks with the ruling Zimbabwe African National Union - Patriotic Front (ZANU-PF) to stand against Mugabe as an independent.
He has in the past called Makoni a "prostitute" for taking him on and the former finance minister was expelled from the ZANU-PF last month after announcing his challenge.
Morgan Tsvangirai, the MDC leader, has warned that the March 29 poll could be rigged in favour of Mugabe and has threatened to pull out of the elections if presidential ballots are counted at a separate venue from concurrent legislative and local votes.
He told a news conference on Thursday that independent investigations had revealed that 90,000 names appearing on the roll for 28 rural constituencies could not be accounted for.
His MDC has also deplored new electoral regulations passed this week by Mugabe which allow police officers into polling stations during the elections.
The regulations allow policemen in polling stations to assist illiterate or physically challenged voters.