For whom the summit tolls: who pays for better roads?

As summits go, the one at Magor services got slightly less media attention than the one hosted by David Cameron in Northern Ireland.

But if you use the M4 regularly, for business or pleasure (if that's possible), then the outcome of the Magor summit will be of interest.

Of course, it may have been a piece of political theatre scheduled ahead of good news on the subject in Chancellor George Osborne's spending review statement next week.

It's now more than 18 months since Mr Osborne promised to work with the Welsh government to improve the M4. It's a policy so popular the Treasury announced it again in this year's budget statement.

The Tories present at yesterday's summit hope they're pushing at an open Treasury door. There remain questions over how any improvements would be funded. Welsh ministers rejected a reported (Mr Osborne said "mis-reported") suggestion that a relief road be funded by tolls.

Today, MPs on the Welsh affairs committee had a chance to grill UK Transport Minister Stephen Hammond on progress. He chose his words very carefully, telling them: "The government has been working with the Welsh government exploring funding options.

"The government has a clear policy not to toll existing road capacity in the UK. The prime minister has said that and the department has reiterated that. Therefore, if there were to be any tolling at all it would be as a a result of an infrastructure upgrade but the government has no plans to toll existing roads and the government's working to assess the recommendations of the Silk commission (on the welsh government's powers) and will respond to that as soon as possible."

Asked if improvements could be funded by toll money from the Severn bridges in future, Mr Hammond suggested that for that to happen the Act that created the current tolling regime on the Severn crossings may have to be extended.

Could the bridge tolls be used as a revenue stream against which the Welsh government could borrow? (Ministers in both governments agreed a deal on borrowing powers in principle eight months ago)

Committee members emerged afterwards none the wiser on that point, although it was striking how often Mr Hammond reminded them how any future deal on the Severn crossings had to reflect the interests of road users in England as well as those in Wales.

The Welsh Conservatives (who want to privatise Cardiff airport) want to nationalise the Severn bridges, including the one that is wholly in England. This seemed to be news to Mr Hammond, who repeated the UK government's policy when asked if he agreed with colleagues in Cardiff.

Tory MP Simon Hart had a simpler question for him about the cost of the tolls: "Who comes up with the £6.20 or £12.40 or £18.60 figures? As a road user the most annoying thing I find..I'd rather pay £6.50 or 13 quid than try to find these multiples clearly dreamt up by somebody who doesn't drive a car."

Mr Hammond told him: "I'm not sure they drive a car or not. I take the point those are inconvenient numbers. My understanding is that's the concessionaire's decision to set those prices."

Tolls are increased in line with the retail price index every year. Presumably, Severn River Crossings plc would not complain should Mr Hart suggest they keep the change.