The fact that you subsequently got a refund, doesn't alter the amount that you paid for the ticket. Neither does it affect the price of the ticket, which is what delay repay is calculated on.
The refund does not mean that you now have some phantom ticket of lower value.
Indeed. And fundamentally, if you submit your Delay Repay claim first then there is absolutely nothing in the NRCoT that says you cannot subsequently claim the partial downgrade refund.
The contractual position is that if first class isn’t available you get a refund for the difference between first class and standard class (but note that the contractual entitlement is based on the walk up standard fare- lots of first class fares are less than that, and TfW seem to be being more generous with their first class refunds than the contractual minimum).
The contractual position is not limited to what the NRCoT says. You have to consider the terms implied into the contract by the Consumer Rights Act - wherein a price reduction would be applicable (i.e. a partial refund) in the case of the service not being provided with reasonable care and skill, or not in accordance with implied terms of the contract (for example that the advertised first class accommodation will actually be provided).
The CRA states that a price reduction will be of a "reasonable" amount. Clearly comparing a first class Advance to the equivalent tier of standard class Advance is a reasonable way of performing such a calculation.
Another reasonable approach would be to say that you take the multiplier which TfW generally applies to first class fares as against standard class fares (approximately 1.6 times) and apply a commensurate price reduction.
Clearly, comparing a first class Advance to a walk-up fare which the customer never held, and whose flexibility they never benefited from, is not going to result in a "reasonable" price reduction.
So TfW are not being more generous than they are obliged to be. They are simply complying with the Consumer Rights Act.
The contractual position is that if your train is delayed you receive compensation for the amount you paid.
Assume you paid £100 for your first class ticket and the standard class ticket was £60.
If first class is not available, you are entitled to a refund of £40. This means that you have only paid £60 for your ticket.
This is where you're going wrong. The fact that it downgrade refund has been paid does not alter the fact that the price of the original ticket is £100. Moreover, if the Delay Repay claim is made first (as seems to be the case here) then at that point no downgrade refund has been paid, and clearly there is no basis to calculate it on anything other than the £100 ticket cost.
The OP is then fully entitled to make it a downgrade claim, as there is nothing under the NRCoT or consumer rights law that says that contractual liquidated damages (compensation) already paid must be set off against a refund due.
Therefore, any compensation due would be based on that £60. You still get £100 back: £60 for the delay repay and £40 for the first class.
The fact you’d have still got £100 if first class had been available is neither here nor there, as you’d have paid £100 not £60. Whether this is fair or not is also irrelevant.
If anyone thinks that the legal and contractual position is different, I’d be curious why they think that. Even the Consumer Rights Act is largely based on people getting their money back, nothing more.
They are two different remedies under separate regimes.
The Consumer Rights Act/NRCoT gives the entitlement to the downgrade refund.
The NRCoT/Passenger Charter give the right to Delay Repay (i.e. contractual liquidated damages). These happen to be calculated based on the cost of the ticket, but could just as well be calculated on any other measure, such as an amount per minute of delay (this is the case for c2c on smartcard seasons).
Neither remedy states that they are to be netted off against each other or capped in aggregate. The NRCoT simply states that the total amount of
delay compensation is limited to the cost of the ticket. The NRCoT do not state that the total amount of
all claims arising out of a journey are limited to the amount paid. That is the key point here, TfW have an idea that the cap on total delay compensation also applies to other claims when this is simply not the case.