Tracking / alignment problems

[Repromanded]

Vectra c 1.9cdti 120 with 215/55/16 alloys on. Recently bought the car and had the alloys in the shed but 3 tyres needed changed.

So I had 3 new tyres fitted and wanted the tracking doing as I was having a bit play in the steering when going round roundabouts.
They stuck it on the ramps using a laser system on the front with plates on the rear but afterwards the steering wheel wasn't straight and it was pulling to the right so I took it back. Although I realised the rear tyre that wasn't changed was low (under 20psi) and topped it up.

They showed me what they were doing this time and the rear plates read 6.5 but the toe in/out plates on the front read - 1 for one side and 1 for the other. I asked him to set it at zero but they said it uses the datum from the rears or something so he couldn't?

It's still pulling to the right somewhat, although the wheel is straight now.
What do I do now?
Is it a problem with the car?
Should the toe numbers be the same for both sides? Would this change the rear plate numbers so they weren't the same both sides?
What does he mean about the datum of the rear wheels?
Do the rears have no adjustment?

Cheers, Andrew

[GreenV8S]

Repromanded said:

I was having a bit play in the steering

If you've got play (backlash) in the steering/suspension you need to sort that out and I'd suggest it's pointless to mess about with the geometry until you have done.