Hi AdamLT
Welcome to the mad house. The only real way to see if you can pass the tests is to actually do them. You can do just the colour vision tests at the CAA in Gatwick at £28 cost. If you pass you can go and do the full class 1 medical (on another day) and happy days. If you fail they will class you CP4 colour unsafe. You can still get a class 1 medical, but will be limited to air work such as instruction during the day - no public transport!! However the CAA only do the Baynes and Holmes Wright tests if you fail ishihara. There are anothe 2 tests acceptable to the JAA which are the Nagel Anomalascope and the Spectrolux. These you will have to go abroad for, but if you pass the CAA will remove your restriction and class you as CP3 colour safe.
The City Uni does not give the exact tests the CAA do, so I would say get to Gatwick and give them a go - you only have £28 to loose.
All the best mate