Callanan - who lost his seat in the European parliament at the weekend - is being touted within Conservative grass roots circles as having both the right "centre of gravity" on British EU membership and "the balance needed to do the job" as UK premier David Cameron seeks to build up member state support for deeper EU reform.
In an article on Tory grandee Lord Ashcroft's influential Conservative Home website today, the 52 year old Callanan is championed as having, "first-hand knowledge of the way the EU institutions work".
The website's editor, Paul Goodman, argues that Cameron should consider Callanan for the post of British commissioner due to his decades long experience in the European parliament as an MEP, as Tory group leader, "and, more importantly, [as leader] of the European Conservative and Reformists (ECR) group, set up to provide a centre-right, non-federalist alternative to the EPP".
"His centre of gravity on Britain’s membership is roughly the party’s centre of gravity"
"He was a driving force behind making the ECR group work. He knows how the parliament and the commission work. Downing Street and Conservative MPs know him [and] his eurosceptic views are long-standing, deeply-felt and real".
Goodman adds, "His centre of gravity on Britain’s membership is roughly the party’s centre of gravity. Yes, he has just lost a Euro-election. But he won three others."
Separately, but also published today, the Telegraph's political editor James Kirkup also sets out the case for Callanan, arguing that, "He’s well respected in Brussels and popular with party colleagues: just the balance needed to do the job as David Cameron hopes to undertake his great renegotiation."
Reports in the British press last weekend suggested that Cameron is set to nominate Andrew Lansley the current leader of the UK House of Commons as the next British commissioner.
However the so-called UKIP 'earthquake' that saw the conservatives pushed into third place in the European elections on Sunday, may prompt a change of heart from the British PM, as he faces pressure from within his party to press forward with EU reform.
"Whoever is nominated as UK commissioner will face a tough time in the European parliament confirmation hearings in the autumn. However, the parliament doesn't usually go after one of their own"
Appointing a serving MP would also automatically trigger another showdown with Nigel Farage's UKIP.
Avoiding a potentially damaging by election defeat - both Goodman and Kirkup acknowledge that putting forward a sitting British Conservative MP while UKIP are currently riding high in the polls is problematic – could help propel Callanan forward as a serious contender for the post.
"Nominating Martin Callanan wouldn't be out of the realms of possibility", an ECR source told the Parliament Magazine.
"It avoids a by-election and whoever is nominated as UK commissioner will face a tough time in the European parliament confirmation hearings in the autumn. However, the parliament doesn't usually go after one of their own."