http://www.dailymail.co.uk/news/article-2570335/Former-British-Ambassador-Moscow-warns-Russia-invaded-Ukraine-difficult-avoid-going-war.htmlThere's your link above:
The U.S. and Britain have both made crisis phone calls to President Putin to urge him not to intervene in Ukraine's Crimea, with the White House warning him it would be a 'grave mistake'.
NATO also asked Russia not to take action that could escalate tension. However Moscow responded by telling the organization to 'refrain' from provocative statements on Ukraine and respect its 'non-bloc' status.
Sir Tony Brenton, who served as British Ambassador from 2004 to 2008, said that war could be an option 'if we do conclude the [Budapest] Memorandum is legally binding.'
It promises to protect Ukraine's borders, in return for Ukraine giving up its nuclear weapons.
Today Kiev has demanded the agreement is activated after insisting their borders had been violated.
In response Mr Brenton said in a BBC radio interview: 'If indeed this is a Russian invasion of Crimea and if we do conclude the [Budapest] Memorandum is legally binding then it's very difficult to avoid the conclusion that we're going to go to war with Russia'.
Ukraine accused Russia of a 'military invasion and occupation', saying Russian troops have taken up positions around a coast guard base and two airports on its strategic Crimea peninsula.