There has been much speculation on what Russia's motives might be but it's almost certainly an escalation of the EU's attempts to extend its borders east into Russia's sphere of influence with the attempts to switch Ukraine's allegiance from Russia to the EU. The EU sees Ukraine as the jewel in the crown of the former Soviet states in eastern Europe and with most of the Russian gas imported into Europe via Ukraine, it is of great strategic importance. Expansion into eastern Europe and Ukraine's vast wealth of natural resources is so important to the EU's empire builders that they're prepared to start a Second Cold War over it.
The Ukrainian president says that Ukraine's interests lie with Russia but its government wants to get its hands on EU money (or more accurately, our money). There have been continuous protests in Kiev organised by the europhile lobby and supported by the EU to try and overthrow the president and start on the disastrous path to EU membership.
The fact that there was only one operational warship available for the whole UK is a bit concerning but of course we can rely on the French loaning us that aircraft carrier if the Russians invade ...