A 12-year-old girl from Torbay in Devon is among the new cases. She travelled on the same flight from Mexico as the Scottish couple confirmed with the virus on Monday.
A 41-year old man in Birmingham and a 22-year old from London have also tested positive for H1N1.
In addition to ordering the extra anti-virals, health secretary Alan Johnson also announced that television and press adverts will run from tomorrow to help inform the public how to lower their risk of developing swine flu.
Leaflets about the swine flu outbreak and how to prevent its spread are to be delivered to every household in the UK in the next few days.
The DoH is also expected to announce that it is increasing the stockpiles of facemasks, which are likely to be issued to GPs and nurses on the frontline.
Health officials in the UK are bracing themselves for more suspected cases, with Gordon Brown expected to be briefed today on the latest developments by the chief medical officer (CMO) for England Sir Liam Donaldson and health secretary Alan Johnson.
Meanwhile, an editorial in The Lancet suggests that the outbreak in Mexico might have started as early as 18 March, when authorities began detecting a surge in influenza-like illnesses in the country.
The Lancet calls for home isolation, combined with other measures of social distancing, as the most likely way to stop the spread of swine influenza.
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