The following companies have the option to cover this
http://www.google.co.uk/search?hl=en&q=%22annual+travel+%2B+45+days&btnG=Search&meta=cr%3DcountryUK|countryGB
http://www.google.co.uk/search?hl=en&q=%22annual+travel+%2B+50+days&btnG=Search&meta=cr%3DcountryUK|countryGB
http://www.google.co.uk/search?hl=en&q=%22annual+travel+%2B+60+days&btnG=Search&meta=cr%3DcountryUK|countryGB
http://www.google.co.uk/search?hl=en&q=%22annual+travel+%2B+90+days&btnG=Search&meta=cr%3DcountryUK|countryGB
Personally I would avoid any of the policies that are underwritten by Axa or White Horse (You can find out who the underwritter is (Insurer) by clicking on the "Summary of Cover" or "Policy Wording")
I find Fortis are very good on claims, if you take a policy out through a broker for Fortis there policy would normally cover having to cancel due to advice from the government not to travel to a region due to Swine Flu.
Bear in mind that as Swine Flu is a "Known Problem" now there is a chance they will not pay out although the soon you buy cover with them or another company that includes cover the better your chances are they will cover it.
http://www.fortisinsurance.co.uk/policyholders/how-to-buy/
(Copy and paste the links)
Or follow the advice Maxine gives you