By Dr David Whitehouse BBC News Online science editor

UK scientists will benefit tremendously by joining Eso, Europe's premier astronomy club - but they also know membership will bring some pain.

It won't always be a bed of roses, but we are starting off on the right foot

Catherine Cesarsky, Eso director general

Ian Halliday, chief executive of the Particle Physics and Astronomy Research Council (PParc), the funding body behind Britain's access to the European Southern Observatory's (Eso) suite of large telescopes, says savings will have to be made.

PParc has to find an entry fee of �80m and �12m a year thereafter. The government has helped but PParc has had to tighten its belt.

Dr Halliday told a media conference: "We've saved some �5m by cutting the operating costs of existing telescopes. We are scaling down the use of our existing telescopes."

But Dr Pat Roche, of Oxford University, told BBC News Online that the positive aspects of joining Eso and gaining access to its world-class telescopes far outweighed any short-term cutbacks. "The future is very bright," he said.

Historic setting

To explain the case for joining Eso and getting time on its impressive telescopes in Chile, astronomers gathered in the historic setting of the Great Star Room, or Octagon Room, of the Royal Observatory Greenwich, which was once part of the house of John Flamsteed, the first Astronomer Royal.

Lord Sainsbury: Times have changed

Why had it taken so long to join, Dr Halliday was asked? Was this not another case of Britain being late in signing up to a European institution?

He partially agreed. "The reason it has taken a while is that policies that were remnants of the British Empire played some kind of role," he said.

Lord Sainsbury, the government Minister for Science and Innovation, gave his full support to Britain joining Eso. He was quick to emphasise that past attitudes to European co-operation were no longer valid.

"With hindsight you can always see a time when you could have done something else. We thought we could go it alone. It looks different today," he said.

Pain and gain

Dr Gerry Gilmore, of Cambridge University, and UK member of the Eso Council, looked back at when it became imperative that the UK should become part of Eso.

Gerry Gilmore: The VLT has made the difference

"The big change was the construction of Eso's Very Large Telescope (VLT) at Paranal in Chile," he said. "Before the VLT was made, Eso was not in front. But the VLT changed all of that. With it they forged ahead of us."

But finding the subscription to Eso will not be easy.

Dr Halliday said: "There is some pain but this is change. The pain will be in terms of redundancies but there is gain as well in terms of new opportunities.

"The UK's money is making all the difference to Eso. Effectively, it is of the right order of magnitude to pay for the new microwave observatory, Alma. We are all very excited about that."

'Right foot'

Dr Catherine Cesarsky, director general of Eso, was full of optimism for Alma.

"I'm delighted that the UK is entering Eso," she told BBC News Online. "We are bringing in one of the strongest European communities in astronomy, and since we are the strongest ground-based astronomy organisation in Europe - and probably the world - it makes sense.

"I would say that if the UK didn't join, it would lose its place in European astronomy and world astronomy.

"Entry also means a steep increase in the Eso budget of more than 20%, so that makes it possible to get on with Alma without any country having to make large sacrifices.

"I think both sides are happy. I'm sure that there will be things to discuss. It won't always be a bed of roses, but we are starting off on the right foot."