Passenger satisfaction with Britain's railways has suffered a "significant decline" over the past 12 months, according to a transport user watchdog.

The proportion of passengers satisfied with their journeys fell from 83% to 81% in the latest autumn survey of 29,000 people by Transport Focus.

Punctuality and reliability of services was the factor showing the largest deterioration, down from 78% to 73%.

Public transport campaigners claimed the results show more emphasis should be given to short-term investment projects.

Lianna Etkind, of the Campaign for Better Transport, said: "This survey confirms passengers are paying through the nose for a shoddy service, and the Government appears not to care as long as the money keeps rolling in.

"There is no point spending billions on increasing capacity whilst ignoring smaller scale investment in reliable infrastructure."

Shadow transport secretary Andy McDonald said: "The results of this survey expose the failure of our privatised railways.

"With promised upgrades delayed or cancelled and fares rising way ahead of wages, it's disappointing but not surprising to see passenger satisfaction down."

The rail firms suffering the largest drop in satisfaction were Southern (down 12 percentage points to 65%), ScotRail (down seven percentage points to 83%) and Great Northern (down seven percentage points to 78%).

Passengers using Hull Trains are the most satisfied in the country at 97%, followed by Heathrow Express (96%) and Merseyrail (95%).

Transport Focus chief executive Anthony Smith said: "The results around the country are disappointing. Scottish passengers and those travelling in peak hours in London and the South East are bearing the brunt of poor performance.

"The timetable on parts of the London and South East's railway can be a work of fiction which passengers cannot rely on. As passenger numbers rise, parts of the rail network will remain brittle until welcome improvements are in place and working."

Analysis by the watchdog found that satisfaction is "significantly lower" for those passengers who travel into London during peak hours.

Punctuality, value for money and dealing with delays for peak-time passengers are particularly low for certain rail firms:

:: Punctuality on Southern - 30%

:: Value for money on Gatwick Express - 12%

:: Dealing with delays on Southern - 12%

Southern passengers have suffered months of disruption because of a row between the company and trade unions over the role of guards and driver-only trains.

Jacqueline Starr, managing director of customer experience at the Rail Delivery Group, representing train operators and Network Rail, said: "We know we must do better.

"We're sorry when customers don't get the service they expect, including those affected by strikes. Everyone in the railway is working hard to make train journeys better from start to finish."

Rail minister Paul Maynard said: "We recognise that levels of passenger satisfaction on Southern and Thameslink are not where they should be, despite no significant change in satisfaction across most other franchises.

"Improving rail services for Southern passengers is a priority for the Government and we are committed to a railway that delivers the timely, modern and convenient service passengers expect.

"We are funding improvements to the network's infrastructure, including £300 million through Network Rail to boost resilience on the Brighton main line - this includes replacing old tracks, points and signalling.

"It is also worth noting that this survey was conducted very soon after a long period of disruption to deliver improvements that passengers had asked for at London Bridge station.

"Passengers will now benefit from improved access to platforms, information and facilities and will see even more benefits when it fully opens in early 2018."