Rail travellers have suffered a "pre-Christmas fortnight from hell" because of signal failures, staff shortages, overcrowding, congestion and other incidents, it has been claimed.
The Rail, Maritime and Transport union said a spate of problems on Britain's "over-stretched" railways in recent weeks should fuel demands for the system to be taken back into public ownership.
General secretary Mick Cash said: "The scandal of Britain's privatised, rip-off railways has seen a further round of problems this morning wrap up another blast of chaos for passengers.
"The hard fact is that if the billions that have been bled out of our railways through two decades of privatisation had been invested in capacity, staffing, maintenance and upgrades, we would not have this daily chaos that has turned our transport services into a global laughing stock
"To make matters worse, the extortionate fares in this country are subsidising domestic rail services across Europe with over three-quarters of Britain's train operations owned by overseas state companies.
"To pile on the misery a new year fare hike is looming which will hit those on low to average pay hard while the private train companies are laughing all the way to the bank."
Fresh problems on Wednesday included a fault with the signalling system near Chippenham which caused disruption to Great Western journeys between Bristol Temple Meads and Swindon.
A temporary shortage of train crew again caused disruption to Southern services, with some trains altered or cancelled, which is expected to continue all day.
South West Trains said a tree that fell on to the London-Portsmouth line on Tuesday, causing delays and disruption to its services, was on private land.