Although the train was cancelled, alternative transport (a rail replacement bus) was provided, so you may claim compensation for the delay to your journey, and also the difference paid between 1st class and the equivalent Std class fare for the journey you made.
You are indeed entitled to compensation for this - the difference between the cost of your first class tickets and the equivalent standard tickets - in addition to compensation for the delay in line with the normal 'Delay Repay' scheme principles.
Was the first train one that was scheduled to have first class at the point you booked?
What time train was it that you were scheduled to take? It is possible on a number of routes to buy a first class ticket despite some or all services not having first class. You only have an entitlement to the difference where the service was originally scheduled to have first class.
Please provide the time of train you intended to take (even if one was not 'booked' - what time you turned up at the station should be enough to work out what service you should've been on). It is also important to know what time you arrived at your destination or no compensation claim for delay can be processed (as how will they know what they delay was?).
If this were your experience... why book a First Class ticket?
All trains on this route convey First Class accommodation. It would be fairly unlikely for any rolling stock that doesn't have it to go this way but not impossible.
That's funny because although all trains on from Cambridge to London Liverpool Street do have First Class, none of thrm have conductors.
You've been asked three times now what time you actually arrived. Since you seem either not to know, or to be unwilling to say for some reason, I would suggest we can be of no further help.
