It will take five years and the drilling of 20 to 40 fracking wells to judge whether the UK has a viable shale gas industry, the chairman of the only company yet to have used modern hydraulic fracturing techniques here has told the Guardian.

Lord Browne of Madingley, former chief of BP and now chairman of Cuadrilla, said the work must be done, because exploiting shale gas was "a national imperative".

He said the process would take so long because of the UK's strict planning laws. "We have very tight regulation, particularly on planning permission," he said.

Browne, who is also a government adviser on business, was speaking on the fringes of a debate on fracking held by the thinktank Policy Exchange. He said that the UK had the potential for a large amount of shale gas exploration, but that aspiring companies would need much more information on whether the gas reserves are economic to exploit, and that could only come from further exploration.

"We have an idea of the UK's potential for shale - what we now need to do is figure out how much we can produce economically and how fast, which means wells need to be drilled and need to be fracked – there is no other way to do it," said Browne, who is also a managing partner at Riverstone Holdings, the venture capital firm that backs Cudrilla.

Tony Bosworth, energy campaigner at Friends of the Earsh, said: "Despite all the government bluster about fracking, the industry still doesn't know if it's viable in Britain, and it will take years to find out. And with experts warning it won't cut fuel bills and will do little to tackle climate change, the coalition's shale gas enthusiasm is looking increasingly ill-judged."

He said renewable energy offered a better way to cut emissions: "The solution to our energy challenges is staring us in the face, and we don't need to wait until the end of the decade. It's time to abandon the UK's fossil fuel addiction and invest in energy efficiency and the nation's world class renewable power potential."

Cuadrilla has already spent more than £100m on exploration, the company told the Guardian last year, but so far has only fracked at one site.

Browne said it was vital to the UK's future to pursue fracking, the operation of which on a massive scale has sent gas prices plummeting in the US in recent years. "It is in the national interest of the UK to do something that is good for the UK and fits into the bigger picture [of combating climate change globally]. The US has done this and I find it extraordinary that we should step to one side and let the US and others get on with it. It is a national imperative."

He said that the UK and Europe's current energy mix, in which large amounts of coal are still being used to generate electricity alongside renewable energy, was like being on a diet but eating "lots of salad and then finishing with several scoops of ice cream".

Tankers enter fortified Barton Moss gas fracking exploration facility, run by IGas, in Barton, England. Photograph: Christopher Furlong/Getty Images

Coal use has increased markedly in the UK in the past few years, reaching about 40% of electricity generation despite its high greenhouse gas emissions. That is partly because coal is cheap at present, as the massive exploitation of gas in the US has meant that coal that would have been burned there is now exported abroad.

But Browne was downbeat on the potential for carbon capture and storage, which some experts have advocated as a way of rendering coal and other fossil fuels low-carbon. He said: "Carbon capture and storage (CCS) is a very interesting idea – I tried to do the first CCS [project in the UK, while leading BP] but there was a gap between what it would cost and what we could afford. There are very few places in the world where CCS could be made to work. I would not rule it out but I would not rule it in."

Prof Dieter Helm, an energy economist at Oxford University, agreed: "Don't get terribly excited about CCS any time soon – the volume of [carbon dioxide] gas is greater than the stuff that comes out of the ground. And there aren't enough holes [in which to store the CO2]."

Browne said it was possible to make fracking more environmentally friendly, through capturing any fugitive methane emissions and by using less water, and recycling the water used. "Fracking is not fossilised technology, it is moving to use less water. This technology is not static."

He said that there was no conflict between investment in renewable energy and in shale gas.

Helm said that renewable energy subsidies would be "permanent, not transitory" for current technologies such as on- and offshore wind and solar panels. He advised much larger levels of research and development into new generations of renewable technologies, including geothermal energy and the possibilities of graphene.

Jason Anderson, head of EU climate and energy policy at WWF, said the first priority should be energy efficiency. "The main challenge for Europe is to renovate the 80% of buildings built before we had good energy efficiency standards," he said.