More main line trains could run on time after an announcement of a £35-billion funding package.

The Great Western Main Line between Cardiff, Bristol and London is one of many lines set to benefit from the investment by Network Rail over the next five years.

The main scheme to be put in place will be a re-working of the busy station at Reading, which is currently a difficult bottleneck for trains heading into and out of the capital, as trains heading to London from a number of different lines converge and have to wait . The knock-on effect of the bottleneck is frequent delays on services between London and Bristol, but there is optimism that this will be a thing of the past with the new funding.

Mike Greedy, spokesman for rail watchdog Passenger Focus, welcomed the move but said it could be a long time before the real benefits were noticed.

He said: "This will be a significant investment because Reading is certainly a major bottleneck for people travelling from the South West to London. It's been a thorn in the side for a number of years and the improvements will have a big impact.

"But there will be other developments happening which will impact on passengers travelling to London, so it's going to take a long time before people will see the benefits.

"There is going to be a period of significant disruption."

The news was also welcomed by First Great Western, which will operate its franchise on the line until 2016.

A spokesman said: "Over the past year we have consistently improved the punctuality and reliability of our services, with around 19 out of 20 services arriving on time in March.

"The close working relationship we have built with Network Rail has played a significant part in giving customers some of the best performance figures ever in the region.

"However, we realise there is still much for us to do to deliver more for our customers.

"Network Rail has assured us they will continue to spend additional money on day to day maintenance to ensure the safety and performance of our network.

"While most of the renewal work being carried out is some distance from the Bristol area, work, for example, on the remodelling of the Reading area will bring improved journey times to customers across the region."

These are not the only plans for the future of the Great Western Mainline. The Government has invited tenders for a new generation of hybrid trains, which could run on a combination of diesel and electric, with plans in the pipeline for the electrification of the line in the future.

Iain Coucher, chief executive of Network Rail, said: "Stations will be transformed and new ones built. Speeds will be increased. Bottlenecks will be unblocked.

"Thousands of new trains will debut, services will run more frequently at weekends and at bank holidays. And all this while time keeping is ramped up, costs driven down and safety boosted.

"The last five years has been about putting right the ills of the railway - this has been achieved with train punctuality, passenger satisfaction and railway safety all at record levels and billions cut from the cost of running the railway.

"The next five years will be focused on doing the basics even better and delivering a bigger, better railway for passengers and freight."