Each of these is a refusal this regime lets a counterparty attempt, paired with the answer to it. Reading them before you write is worth more than any amount of polish on the letter itself.
"The delay was caused by Network Rail / the infrastructure manager / a third party"
high likelihoodThe operator points at signalling failure, a broken-down freight train, trespass or someone else’s infrastructure and says the delay was not their doing.
What answers it
Under the contractual UK Delay Repay schemes, cause is irrelevant to your entitlement: the schemes pay on the delay, whoever caused it, and the operator recovers internally from the infrastructure manager. Under Regulation (EU) 2021/782 the railway undertaking is the passenger’s counterparty and only a genuinely exceptional, unavoidable circumstance excuses it — and a staff strike at the railway itself is expressly not one.
"Here is a voucher"
high likelihoodThe operator settles in rail travel vouchers or credit rather than money, often at a discount to what is owed.
What answers it
You are entitled to be paid in money. UK operators must offer at least one monetary method — bank transfer, cheque or refund to the original card — and Regulation (EU) 2021/782 allows vouchers only where the passenger accepts them, meaning you can simply decline and ask for cash. A voucher is worth less than its face value to you and more than its face value to them, which is why it is offered first.
"Your season ticket already accounts for delays"
medium likelihoodThe operator suggests that a discounted season or an annual "performance" adjustment already compensates the holder, so individual claims are not payable.
What answers it
A season ticket does not waive compensation for individual delayed journeys. The schemes set out a pro-rata method for valuing one journey out of a season, precisely so that season holders can claim per delay. Ask them to apply it and to show the calculation.