Get a vacuum bleeder kit from your local motor factor.
https://www.sealey.co.uk/product/5637204666/1l-pneumatic-vacuum-brake-bleeder is what I use (and it can be got cheaper than this I am sure).
If the brakes pump up then there is air in the system. If not then check the length of the pedal to servo operating rod. If that is OK then consider taking off the master cylinder and checking the length of the rod between the servo and the master cylinder piston. There is a post (by me) early on in the technical information thread that may help.