The arguments over affordable life-saving medicines for the developing world intensified yesterday when it was revealed that the multinational pharmaceutical company Glaxo-Wellcome has blocked imports of cheap copies of one of its Aids drugs into Ghana.

The revelation came as South Africa announced it had done a deal with a second company, Pfizer, over supplies of the drug Fluconazole to treat infections such as meningitis that often kill people whose immune systems are wrecked by the Aids virus HIV.

Under pressure from campaigners, who began bringing a cheaper version of the patent-protected branded drug into South Africa which massively undercut the usual Pfizer price, the company has agreed to supply Fluconazole free.

But although aid organisations such as the charity Médecins Sans Frontières (MSF) hailed the deal as an example of what can be achieved if countries show a willingness to turn their back on the pharmaceutical giants and buy copies, Britain made it clear yesterday that it was not in favour of such tactics.

Trade minister Richard Caborn told activists from the London-based organisation Action for Southern Africa (Actsa) that such measures "are not the answer here". Campaigners insist that developing countries must use every possible means to get hold of affordable drugs that can stop people dying.

But western governments say the companies have a right to protection for the drugs they sell at high prices in order, the companies argue, to recoup research and development costs.

The west says the right approach is for countries to negotiate discounts with the companies. But African nations say they cannot afford the drugs even at the discount prices offered in May this year by five multinationals. Only Senegal has so far taken up the invitation to negotiate a deal. The giants take very seriously the threat of competition.

Glaxo-Wellcome has blocked the import into Ghana of a version of its Aids therapy Combivir made in India by Cipla. It is argued by campaigners that impoverished countries faced with a health emergency have a right under international trade legislation to buy generic drugs.

The African Regional Industrial Property Organisation was quoted yesterday as saying that if Glaxo went to court, it believed it would lose. But poor countries fear confrontation will upset relations with the west. Glaxo's spokesman said the company had offered Ghana its own drugs under its "preferential pricing" scheme.

The price for the generic version of Combivir has not been revealed, but generics sell for a fraction of the branded price. MSF has gathered data showing that Cipla sells Fluconazole for $0.64 (45p) in India, compared with Pfizer's price in South Africa of $8.25 and in Kenya of $10.56.

MSF pointed out yesterday that AZT and 3TC, the two drugs in Combivir, are both old and that they were developed with the help of public funds in the United States. Glaxo Wellcome has already made many millions out of them.

"It cannot argue it needs to recoup its investment," said a spokesman. Actsa says that the threat of generic competition made Pfizer lift restrictions it wanted to impose on the Fluconazole it is donating to South Africa.

"At first it was going to be only for meningitis and not for thrush, which affects more people.

The company was dictating how the drug was to be used," said a spokesman. The Pfizer deal was announced the day after South Africa's medicines control council said it would allow generic Fluconazole to be used in the country.