In electoral terms 1997 was the year of the pincer movement.
More anti-Conservative voting took place than at any previous general election, with about 24 more seats reckoned to have fallen to Labour than it would otherwise have won.
Tory Central Office number-crunchers are waiting nervously to see if Labour and Liberal Democrat voters subject William Hague to the same twin squeeze this time round.
Analysis of voting patterns across the UK showed a clear trend of voters backing whichever opposition party was best-placed to defeat the Conservative candidate.
The swing to Labour was greater than the national average (10.2%) in those seats where its candidates entered the campaign second to the Tories, while support for the Lib Dems fell by more than the average.
This produced gains New Labour never expected to make from the Conservatives, like Hastings (Labour swing of 18.5%), Harrows West (17.5%) and East (18.1%), and Enfields North (16.1%) and Southgate (17.4%).
And in those Tory seats where the Lib Dems were the closest contender, support for the challenger rose above the national trend while Labour's support increased by notably less than the average.
Thus Lib Dem gains like Richmond Park (on a 9.7% swing from the Conservatives), Twickenham (8.8%) and Lewes (7.4%).
Voters can generally work out for themselves which way to cast their ballots if stopping the Tory is their aim.
But for this election, William Hague must also contend with a concerted campaign, more organised than at other elections, to maximise the anti-Tory vote.
In much the same way that MPs from different parties "pair" with each other to cancel out their absence from votes in the House of Commons, tactical voting campaigners are organising "vote-swapping" on the internet.
As well as advising voters on where the anti-Tory vote should go in each seat, truly keen anti-Tories can be matched up via email with a fellow tactical voter in another constituency.
In this way, a Labour backer in Kingston & Surbiton could vote tactically for the Lib Dem Ed Davey (majority: 56) while his Lib Dem pair in, say, Wimbledon, could vote for Labour's Roger Casale (majority: 2,990) - as a dedicated local anti-Tory site urges.
Billy Bragg's swapshop
Singer-songwriter Billy Bragg, one of the founders of Red Wedge back in the early Thatcher years, has set up his own vote-swapping website in Dorset.
A resident of the seat won in 1997 by shadow chief secretary to the Treasury Oliver Letwin (majority: 1,840), the traditionalist bard of the left intends to vote Lib Dem on 7 June - and wishes to help others keener to strike against the Tories than back their preferred party.
The vote swapshop he presides over links up with neighbouring Dorset South, where Tory Ian Bruce's majority is a wafer-like 77 votes - and Labour is the main challenger.
To Conservative supporters all this may all seem a little unfair.
Where, after all, are the websites calling for a similar joint attack on Labour?
For there are indeed Lib Dem supporters who would rather back the opposition than vote for Labour.
Unfortunately for Mr Hague, tactical voting as an organised, high-profile phenomenon is a relatively new trend emerging over the past 20 years or so - for most of which the Tories were in power.
As a result, tactical voting has usually expressed itself as Lib Dem-Labour vs the Conservatives.
And in this sense, the Tories are victims of their own past success.