It's a Canadian insurer, so I suspect of limited use to you, but thought I would mention it in case it is in there in the small print! I used to have it on a UK policy as well, a fair few years ago now, it was an insurance through one of the banks (Lloyds) so I am not sure who the underwriter was. It provided for all means of transport - I intially got it because I had a spate of railway delays (getting mainline down to Heathrow) and it covered both train and plane providers.

This coverage is quite common in the UK. As long as I'm on scheduled public transport, train, bus or plane, and I think prebooked, I'm covered for delays.

So I've checked my insurance policy and missed international departure is covered but... but not on the return journey!
So Insurefor Premier at a cost of over £110 for couple cover isn't great. So be warned if you're insured with them.

However, the free travel insurance through our HSBC Advance account, seems like they might cover it.
I've chatted to them and sent off the claim, so fingers crossed.