This article is part of a debate hosted by Compass on tactical voting. You’re warmly encouraged to join the debate at http://compassonline.forumchitchat.com/

Back in the day, when I was lecturing in politics, it was fashionable to explain changes in voting patterns through realignment. The massive vote by the working class for Thatcher was a stark reminder that the traditional patterns of voting based on class or occupation,  housing tenure was broken.

Dealignment has followed realignment. There is much greater electoral volatility and fewer voters with any strong or lasting attachment to the major parties. The challenge for the political parties is now how to win elections when core support is shrinking.

With the 2015 general election too close too call, and with a record number of marginal seats, tactical voting will really come into its own and could be one of the key determinants of the election. In many marginals there will be a plea to keep X out by voting Y. In others will the claim that only Z can win so voting A, B or C is a waste of time. In all cases voters are encouraged to vote tactically.

There are a number of reasons why tactical voting should be encouraged but for me it really is about the failure of our current voting system. More and more seats are being won with less and less popular support and for some this becomes untenable. Sheffield Hallam constituency (which just happens to be where I live) is a case in point. A safe Tory seat was turned into a Liberal Democrat stronghold in 1997 because so many non Tory voters were disullusioned by Irvine Patnick. Labour voters did the maths and switched their vote.

Our current voting system disenfranchises so many that the only recourse people have is to vote tactically.  First past the post is the most unrepresentative of voting systems when you have a multi party state as we now do. First past the post has favoured the main political parties, with a slight edge for Labour, for decades. It’s a winner takes all situation that delivers when you have two contenders but is absolutely unacceptable when you have more than two parties contesting an election.

The fact that so many people don’t vote is partly down to our voting system. This in turn allows some pretty poor behaviour by political parties. General election strategies are  now driven by the need to get out the vote in the handful of constituencies that will determine the final outcome. As the election gets nearer, politicians become wary of going off message or of frightening the horses in those key marginals. It’s dispiriting politics.

There are some 194 seats with majorities of 10% or less (www.bbc.com/uk-politics-25949029). That means a swing of 5% can change the colour of the seat-  and with a highly volatile and less partisan electorate, many more seats are vulnerable.

Given our voting system, I think all that’s left is to vote tactically. I know that for many this is not palatable. I couldn’t bring myself to vote tactically in 1997. I duly placed my tick against Labour and got a Liberal Democrat MP. Actually what we all got in Sheffield Hallam was Richard Allen, an MP who was fantastic.

It’s something worth reflecting on. Maybe the electorate did indirectly know what it was doing, even if the motive was to give Irvine Patnick a bloody nose. It demonstrated that it should not be taken for granted. The consequence is now a seat where turn out matters in what could be seen as a three way marginal.

Tactical voting is just that. Tactical. And it’s a means to an end. Until we get the voting system we deserve, more people will resort to this. It also shows that people won’t be corralled by the major parties in the traditional way. And MPs in marginal seats may well pay the price for this in May this year.