Until now, the debate over the HS2 rail link (which, according to Boris Johnson, will cost £70bn rather than £42bn) has focused mainly on the time we may be able to save on journeys from London to provincial cities, and the potential economic benefits that could come with such savings.

Wrongly so, some experts have said: the real rationale for HS2 should not be speed, but capacity, since studies show that the current west coast mainline will effectively be full by 2030. Only by building this vastly expensive new route are we going to be able to cope with the growth in passenger and freight traffic, they say. But arguments over rail capacity are seldom as clear as Network Rail and others would like us to believe.

When a rail company I worked with, Grand Central, was seeking paths to run trains on the east coast mainline, Network Rail constantly told us that paths could not be found. Yet when experts persistently challenged Network Rail's methodology, it eventually proved that there was capacity after all, not only for the services which Grand Central wanted to run, but also for improved frequencies between Leeds and London being sought by the then franchised operator on that route.

Given my first-hand experience of seeing how flawed rail capacity studies really are, I am convinced that the time is right to consider a radical alternative to HS2, which would create capacity on the WCML to allow for faster trains on that route, as well as future increases in services to Manchester, the north-west and Scotland.

The alternative, which I firmly believe destroys the rationale for HS2, is to make Paddington the new London terminus for fast services to the West Midlands – making use of the terminal's extra capacity, which will be freed up by the opening of Crossrail in 2018, and upgrading the route from Old Oak Common (just west of Paddington) to Birmingham via Banbury and Leamington Spa. One section of this route – from Old Oak Common to its junction, with the line from Marylebone at West Ruislip – currently has a service of just one train a day: no capacity issues there.

This was one of the main routes to Birmingham until electrification of the line to Euston was completed in 1967, when it was relegated to the role of a secondary route. But it has recently been significantly upgraded by its current franchised operator, Chiltern Railways. Potential capacity issues can be solved by reinstating fast through lines at stations that once had them – Gerrards Cross, Beaconsfield, High Wycombe, Bicester North – and diverting north-south freight trains – currently using this route north of Banbury – on to the soon-to-be-reopened east-west route from Oxford to Bletchley, where they could join the west coast mainline, or to Bedford, for the Midland main line.

Further investment would be required on the sections of route from Leamington Spa to Birmingham and between Leamington Spa and Coventry, but the cost of these improvements would be small change when set against the colossal bill for HS2.

Making Paddington the focus for services from the West Midlands would avert the devastating impact of HS2 on the Euston/Camden area in London, where 600 homes are likely to be demolished – as well as on communities and countryside along the proposed line of route. One real bonus would be to give users of these services a direct connection at Paddington to Heathrow Airport and across London via Crossrail.

All in all, it would certainly cost only a fraction of the (rising) cost of the current plan – so plenty of money left over to invest elsewhere. So I would like to challenge any one of our three main political parties to ditch their commitment to HS2, spend up to £10bn on delivering the route outlined above and set aside another £10bn to finance a 10-year programme of route reopenings around the country. This could deliver schemes such as Uckfield-Lewes, Bristol-Portishead, Skipton-Colne, Statford-upon-Avon-Honeybourne, Southampton-Hythe, Bere Alston-Okehampton and at least a score of other long-desired reopenings, each of which would generate significant new journey opportunities around the country and be obvious vote-winners in the constituencies affected.

Politicians of Britain, do you want a sound and popular proposal for your next election manifesto? Here it is.