You say they wouldn't promote you as you could not drive, were you able and did you inform them that you would be able to travel to needed destinations. If so they should not discriminate against you for not driving yourself. (Ofcourse might not be possible in your line of work)
To clarify how long were you working via the agency and how long for the company directly.
And as far as I am aware, everyone who earns over £95 a week and is contracted is entitled to SSP, providing your sick for 4 consecutive days.
Oh and regarding holiday entitlement, there is a minimum right to paid holiday. You are entitled to a minimum of 5.6 weeks paid annual leave (works out to 28 days if you work 5 days a week). However, bank holiday can be included in your leave entitlement.
Edit: Didn't read the post thoroughly, Baj's post is a bit more on topic.