It looks like a Lake and Elliot Millennium MO Series but they had the plug (that's on the front of yours, as does this one) on the side opposite the pump. However I'm sure yours is a L & E. The MO series ranged from 1.5 tonne to 20 tonnes.
The rusty piston doesn't inspire as it need to be smooth to seal properly. So whilst probably 2T when in good condition the state of the piston will probably reduced that capacity. Personally I only use hydraulic bottle jacks at home. For emergency use a screw type is far more reliable and you can get them cheaply off eBay from a Transit etc.