It's been another busy day, which has been largely dominated by the EU summit in Brussels. Here's a round-up of the key developments:

- David Cameron  has accepted it may not be possible to change  the EU's treaties before the UK's in/out referendum, the BBC understands

- The government said it is to delay or cut back a number of modernisation projects planned for Network Rail. Transport Secretary Patrick McLoughlin says  rising costs and missed targets  make the £38.5bn plan untenable

- Former Lib Dem leader Nick Clegg blamed the rise of the SNP - rather than his own leadership - for the party's devastating general election defeat

- The UK  population grew by almost half a million  last year to 64,596,800, according to figures from the Office for National Statistics.

- The number of UK children classed as  living in relative poverty remains 2.3 million, government figures suggest

And finally, SNP MP Mhairi Black - the youngest MP to sit in the Commons for almost 350 years -  has been awarded a first class politics degree from the University of Glasgow.

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The Ministry of Defence (MoD) has failed to meet its targets for recruiting more Army reservists, according to a government report.

The Major Projects Authority - which keeps track of the progress of big government schemes - has rated the "Future Reserves 2020" scheme as "red" because it hasn't met its published recruitment targets.

The scheme aimed to boost the number of reservists while reducing regular forces.

The MoD says it is now making "good progress".

The new chair of the Commons Defence Committee, Julian Lewis, has said it would be "unconscionable" for UK spending on defence to drop below the target of 2% of GDP.

In his first interview since being elected to the role, the Conservative MP said he was "baffled" that David Cameron had not committed to continue meeting the target - set by Nato - beyond the 2015-16 financial year.

Mr Lewis told Parliament's House magazine that the "worsening situation" in terms of global security meant that defence spending should be nearer 3%.

The PM has said the government's plans for future defence spending will be announced in Chancellor George Osborne's autumn spending review.

Image source, EPA

David Cameron has accepted there may be no change to the EU's treaties to accommodate Britain's demands ahead of a referendum, the BBC understands.

Mr Cameron has instead argued for an "irreversible lock" and "legally binding" guarantees that EU law will be changed at some point in the future, says the BBC's Nick Robinson.

No 10 said the PM remained committed to "proper, full on treaty change".

Eurosceptic Tory MP John Redwood said the EU could not be trusted.

Read our story here.

Image source, Reuters

The youngest MP to sit in the House of Commons for almost 350 years has been awarded a first class politics degree from the University of Glasgow.

Mhairi Black won the Paisley and Renfrewshire South seat for the SNP in last month's general election.

The 20-year-old sat her final exam on Scottish politics shortly after being elected.

She will graduate along with the rest of her class in a ceremony at the university on Friday.

More here.

Here's a quick recap of some of the big political stories today:

+ David Cameron has accepted it may not be possible to change the EU's treaties before the UK's in/out referendum, the BBC understands.

+ The government said it is to delay or cut back a number of modernisation projects planned for Network Rail. Transport Secretary Patrick McLoughlin says rising costs and missed targets make the £38.5bn plan untenable.

+ Nick Clegg blamed the rise of the SNP - rather than his own leadership - for his party's devastating general election defeat, in an LBC interview .

+ The UK population grew by almost half a million last year to 64,596,800, according to figures from the Office for National Statistics.

+ The number of UK children classed as living in relative poverty remains 2.3 million, government figures suggest. Work and Pensions Secretary Iain Duncan Smith said UK poverty levels were the "lowest since the mid-1980s" and showed government reforms were working.

Unions, campaign groups and opposition politicians have questioned the government's figures which suggest that child poverty has fallen to its lowest level since the 1980s. 

Labour MP Frank Field, who chairs the Work and Pensions Select Committee, said: "Politicians might understand these measurements but the electorate certainly doesn't. 

"What I hope would interest the electorate is action to prevent poor children becoming poor adults. 

"We must therefore begin talking about, and measuring, poor children's life chances and how they can be improved. It is important that such measurements are accurate, but that they can also safely drive anti-poverty policy." 

Nick Robinson
Political editor

The BBC understands that the prime minister has accepted that it may not be possible to change the EU's treaties - the laws on which it is based - before the UK votes in a referendum on whether to stay in or leave the EU.

In recent meetings with fellow European Union leaders David Cameron has argued instead for what officials call an "irreversible lock" and "legally binding" guarantees that at some future date EU law will be changed to accommodate Britain's renegotiation.

As recently as January Mr Cameron insisted that he would be demanding "proper, full-on treaty change".

Eurosceptics and those who want to leave the EU altogether have always been suspicious that agreements between political leaders can be later undermined in the courts.

They believe that legal or treaty changes are necessary to deliver the prime minister's negotiating objectives - in particular to free Britain from the EU's commitment to build an "ever closer union" of nation states and to ensure that benefits such as tax credits be withheld from migrants who have been in the country for less than four years.

David Cameron's critics may fear that the formula he is now using is a watering down of that commitment and will demand to know who would interpret any legally binding agreement reached between the UK and the rest of the EU.

Downing Street insists, however, that it is simply a reflection of the fact that any treaty change will require a time consuming ratification process in 28 different countries involving parliamentary votes as well as referendums in France, Ireland and Denmark.

They point out that when Ireland had a referendum in 2009 on the Lisbon Treaty all other EU countries had not yet ratified the proposed changes in EU law.

Image source, Other

Jonathan Isaby the chief executive of the TaxPayers' Alliance, has called the HS2 project a "white elephant" in the wake of the news that the government is "pausing" the electrification of Midland Main Line and the Trans-Pennine route between Leeds and Manchester.

He said: "The secretary of state is right to ensure that electrification delivers value for money, but the delaying of this project is in part a result of the billions being put aside to build a high-speed white elephant. If only the same stringent tests ensuring taxpayers' money isn't wasted were applied to HS2."

He added: