Image caption David Cameron said party members' views on the proposals would "inevitably" differ

Tories in the most marginal seats in parliament are urging David Cameron to bring in tougher conditions on housing benefit for some teenage mothers.

The 40 Group also wants the party to make an election promise of a cap on the number of non-EU foreign students allowed into some UK universities.

The group represents Tory MPs from the 40 seats with the thinnest majorities.

The ideas are among dozens featured in a pamphlet, seen by the BBC, which is due to be published soon.

It covers a diverse range of policy areas and has taken a year to compile.

West Midlands MP James Morris, who is one of the authors, described the proposals as "an offering to the prime minister from the battleground".

He said "quite a lot" of the 40 proposals came "from the mouths of swing voters".

'Boris Island'

In a foreword seen by the BBC, the prime minister described the proposals as "interesting" and "valuable", although he added that he thought party members would "inevitably have different views" about them.

The Tory MPs admitted their proposals on benefits for teenage mothers were "controversial", but they said a "more radical approach" was needed to get pregnancy rates down.

They claim the current system has led some young people to think, incorrectly, that they had an automatic right to free housing if they got pregnant, "encouraging them to have a child".

So they suggest "all benefits to teenage mothers should be made on the condition of them living with their parents or in supervised hostel accommodation".

The group is calling for a tougher approach to truancy. It says parents of children who persistently skipped school should have fines automatically deducted from their child benefit.

There was also a slap in the face for fellow Conservative Boris Johnson.

The group wants a new runway at Birmingham Airport to deal with an expansion in air traffic instead of a major new airport in the Thames estuary, favoured by the London Mayor and dubbed "Boris Island".

The pamphlet is an unofficial element of the Conservatives 40/40 strategy to try to win the next general election in 2015.

While Britain undoubtedly benefits from foreign students we must not forget that they are also consumers of housing, the NHS, transport and other national infrastructure 40 Group pamphlet

After last year's autumn conference the party unveiled a plan to retain its 40 most marginal seats - some of which the authors of this pamphlet represent - and win a further 40 of the most marginal seats held by Labour and the Liberal Democrats.

Part of that strategy focuses on a big push in the north of England where the Tories have been hit hard.

The idea of moving to regional pay in the public sector is roundly rejected.

The chancellor outlined plans to consider the controversial change in the Budget last year, which could see people in areas with a lower cost of living awarded smaller pay deals.

George Osborne subsequently changed his mind and the government has stuck with national pay deals for public workers.

The group has also called for more civil servants to be moved out of London.

And the chancellor also comes under renewed pressure to scrap higher rate tax relief for people paying into a pension.

The group suggests that as one part of a major overhaul of pension provision.

It is a move which could also insulate the Conservatives against claims that they have favoured the wealthy in some of their changes on tax.

One of the pamphlet authors told the BBC that no suggestions were left out because they were considered too radical or controversial.

But several words that are noticeably absent are "UK Independence Party".

The group does not mention UKIP but it is clear it has Nigel Farage's party in its sights.

It is very hostile to renewable energy like wind farms - UKIP has made opposing wind farms a central plank of in its campaigning in some traditional Tory areas.

It calls for a rethink on government subsidies for renewables, instead favouring a big push on shale gas and even geothermal water heating.

Foreign student cap

A major suggestion on immigration comes right at the end, with a cap on non-EU foreign students allowed into some universities.

They write "while Britain undoubtedly benefits from foreign students we must not forget that they are also consumers of housing, the NHS, transport and other national infrastructure".

But the limit will not apply to the top universities.

Sensitive to strong criticism - some of it from within the coalition - about the negative effects on universities and industry of an immigration cap, they suggest that the top 30 institutions would be exempt.

There is a nod too, to trade away from the EU.

The UK should look to capitalise more on its historical links with the Commonwealth countries, the 40 Group says, which is something Mr Morris described as "possibly a neglected network".

There are signals that the group's ideas are being taken seriously by Tory high command.

The BBC understands that the prime minister's new policy chief Jo Johnson has had "early sight" of the pamphlet and it has been passed on to some of his policy groups.

He is expected to meet some of the authors later this week.