The average age of trains in London and south-east England is 19 years old, an investigation has found.

Rolling stock of British trains nationwide is 21 years old on average, according to the Office of Rail and Road (ORR) statistics.

This is the oldest in at least 15 years, the furthest back publicly available records go.

The ORR said older trains can result in less comfortable journeys, poorer reliability and worse performance than modern versions, although it also noted that older rolling stock can be refurbished.

Rail fares increase by an average of 2.3% across Britain from Monday.

Ed Cox, director of think-tank IPPR North, said: "It is little wonder that Britain lags behind other developed nations when commuters pay through the nose for decrepit trains."

Mick Whelan, general secretary for the train drivers' union Aslef, said: "The problem with privatisation is that it was meant to drive private investment through competition and that has never happened.

"Therefore all we do is retrospective make do and mend in response to population growth and economic need the UK will always be decades behind affordable fares and decent rolling stock."

Lianna Etkind, public transport campaigner at the Campaign for Better Transport, said the current age of trains "exemplifies the lack of public and passenger involvement" in the network.

She said: "We need a strategy from the Government which involves passengers and the wider public in decision making, makes clear what their future plans are on things like electrification and clarifies the roles of the rolling stock companies, the train operators and the Government in paying for updated rolling stock."

Christian Wolmar, railway historian and writer, said investment in new trains in Britain is "very lumpy" because it "isn't properly planned and we don't really have a principal domestic supplier".

He said: "If we had a sensible process we would have a steady, smooth production line that we operate all year round, producing rolling stock at regular intervals.

"The whole thing would be rational and much cheaper."

A Department for Transport spokesman said: "We are delivering the biggest rail modernisation programme for over a century and will be rolling out more than 5,000 carriages over the next four years which offer more seats, wi-fi and air conditioning.

"South West Trains will start testing the first of 150 new carriages in the new year and the first new trains on the Great Western mainline will begin operating next summer, before they are brought in on the East Coast route.

"Through rail franchising, we also expect the rail industry to come up with more proposals to introduce new carriages and improve services."