I had water pouring out the top of the tank where the release valve is (I presume), have turned the machine off now and the water supply. Is the machine completely scaled up inside the tank hence this problem?
I would really appreciate some advice?

Was the machine hot or cold?
Cold, check the fill valve
Hot, what was the gauge pressure? Check the pressurestat.

I photo would help to clarify what's overflowing, but my guess is that after 20 years, the autofill probe has been slowly coated with scale over time, leading to an ever rising steam boiler level. Eventually the boiler overfills through the vacuum breaker or pressure safety release valve. I recommend taking it to a qualified repair technician for long-overdue descaling and maintenance.

machine was hot.
I did not look at the pressure valve because when i was called over the machine was pouring out water from the valve on the top of the main tank as shown in the photos of the other cimbali m20, someone is restoring.

i have someone coming out tomorrow morning to look at it, in all previous services it has been the descaling that is required. The machine is old but I just love the old style look of it.

I am probably going to have to get a new 2 group machine and so I would really appreciate some sound advice as to which machine to buy. Also is it worth me spending £450.00 plus VAT having this serviced or should i just part exchange it.

once again many thanks for coming back so quickly

wrattens

At that price of a service call you could enroll in an espresso service class in Italy and get a nice vacation at the same time! Seems past time to learn how to service and repair the machine...or get in to the espresso repair racket yourself.

Antivac valve not closing? Scaled up probe? Spade connector not attached to probe (I have been guilty of that one..)
Gicar box faulty (expensive). One of the spade connectors not attached properly?

Water will come out a valve on top of the boiler in two places- the anti vacuum valve or the pressure relief valve. From your description the source of the water is not important. The cause is an overfilled boiler as has been mentioned above.

The first thing the tech should probably do it remove the water level sensor to check for scale. While (s)he has that out an inspection with a strong light or even a video probe will reveal the condition of the inside of the boiler as well. The boiler probe wire should then be grounded in the machine and the machine turned. If it tries to pump more water then the Gicar is toast or there is some corrosion somewhere on an electrical lead. If the pump does not run with the lead grounded then scale is likely the problem.