FLD120

Contact www.linear-logic.com and check out their ScanGaugeD diagnostic tool. I am going to get one for my '02 FLD 120 DD 12.7 Series 60. I contacted the company and was told this was the model that would work for this truck. I use a ScanGaugeII for an '06 Ford F350 6.0 PowerStroke Diesel, and am very pleased with it. It costs around $160.00 US. You can order it off of Amazon.com,,,I don't know about shipping costs to U.K. This diagnostics tool does not let you program the codes...if you want that feature you will need to spend about twice the amount. You should be able to find a source over the internet.
As far as your question as to disconnecting the idle time shutdown system....I am not knowledgeable about that. Perhaps you could download the operator's manual from the CAT website and get the answer there.