given the time you posted this is probaby to late, but might help others, if you are going to work in the
UK you will need an national insurance number, this is essential a SIN and does qualify you for basic heath services (NHS). Another thing i found out is certain travel health insurances only cover you if you are covered by your provincial health. Manitoba Health (where i'm from) only covers you for 3 months after you leave the country for an extended leave, so be careful how much insurance you buy, as it may be void after a certain point in time, and you won't be able to get a refund.