Helping friend with luggage at London Euston

Ticket barriers still have to be manned, because a human is still needed to deal with tickets that have got demagnetised, those where the magstripe was never correctly written in the first place, creased/crumpled tickets, jammed readers, and so on.

Cambridge has a CTA, and I've never been refused access without a ticket to the platform when I had a reason to want to go (helping with luggage / meeting elderly or young travellers / confirming someone departed on the right train / etc.). The person manning the barrier just overrides the gate so I can enter without a ticket, then remembers me and lets me out when I reappear a few minutes later. I can confirm that platform tickets no longer exist, because I asked.

Ask (for access) and ye shall receive, I strongly suspect.

It is actually in theory still possible to get a platform ticket at most stations, but I can count on one hand the number of stations where I've required one to go through the barrier without catching a train (but I did once meet someone who collects platform tickets and had managed to get one at almost every station!).

My inclination is the same as in MadHatter's answer - to go to the barrier (some platforms have barriers, some platforms have gates staffed by Virgin employees checking tickets). Best case, it won't be manned and you'll just be able to walk through. I'd expect in most cases though the person will understand you're helping someone with luggage and let you through. You can try to buy a platform ticket from the ticket office but it's unlikely to make a difference between not being allowed on the platform and being allowed on the platform (I've certainly not heard of it doing so at Euston particularly in recent years). I imagine at Euston they get many such requests due to the number of people who will be travelling long-distance, so I imagine they'll be used to granting them. Worst case, I imagine they'll have a member of staff available to give such assistance in the event that they deny you access to the platform.

Your reference to CTAs is not strictly-speaking relevant because Euston is not a Compulsory Ticket Area to my knowledge (someone correct me if I'm wrong), even though it might act like one in practice because of the barriers!

The issue to bear in mind at Euston is that the platform numbers for many services are not announced until a relatively short time before departure, maybe ten minutes or so. Also, there's a separate entrance for each platform or pair of platforms (apart from 1-3 and 8-11 which are entered via automatic gates) and the gate may not be staffed and opened until that time.

This means that you won't know where you need to go or which staff member you will need to ask until shortly before the train leaves, and at busy times you will be among a large number of people queuing to get from the concourse on to the platform. So I would definitely advise being there in good time to check whether you can buy a platform ticket, because if you are refused entry to the platform without one you may well not have time to go back and get one.

The fact that everyone else will be boarding the train at the same time means that if you are refused entry to the platform I think there's a fairly good chance that your friend will be able to ask another passenger to give him a quick hand with his luggage - unless he's travelling on a busy route at a busy time, such as a Manchester or Scotland service on a Friday evening, in which case they may be more concerned with getting on as fast as possible themselves for the best chance of a seat. If that's the case you'll definitely do well to try and be at the front of that queue.

I dealt with similar situations several years back at a different station.

What I did was trough a gate but make sure I nod my head "Hi" to a member of staff, on my way back I went back trough the same gate. The guy started asking me for my ticket, but by the time I opened my mouth to say "I was never on a train, just sending someone else off" He remembered he just saw me several minutes ago and let me pass.

As a data point, we had no problems, got my friend and his luggage onto the train with no difficulty.

This is what actually happened on the day:

1. Park in underground car park at Euston. This car park will be closed from 15th Oct 2018 due to HS2 construction - parking would then be much less convenient.
2. Trailed our way to the lift seeing no trolleys or signs for the same. Later, I heard that there are trolleys to be had near the taxi rank.
3. Lift to concourse, still no trolley.
4. Various brands of ticket machine to be seen, the ones we tried had no apparent way to buy a platform ticket.
5. Went to ticket window and were were told just to ask person at barrier.
6. Friend was travelling to Manchester on Virgin trains - other brands have different procedures. For the Manchester train, platform is shown. Join queue. Two staff scanning barcodes, no auto barriers here. Ask permission to help friend to train: no problem, go right ahead.
7. Deposit friend at their seat, luggage in the rack. All good.
8. Go back past bar code reading staff, say thank you, they remember me and wave me on my way.
9. Get stuck in unstaffed car park!

Net: If there are trolleys they are not easy to find. Virgin platform staff are helpful and seem happy to allow people to help with luggage. If one can get a platform ticket it's not obvious from where.