By political editor Paul Francis

When Gordon Brown announced today the general election will be held on May 6 Kent was firmly in his mind as a key battleground.

No surprise then that his first stop on the election campaign trail is Medway.

Today's announcement triggers what most expect to be the closest-fought campaign in years.

Should the results next month mirror the current polls, the political map of the county could turn completely blue for the first time since Margaret Thatcher’s heyday in the 1980s.

Labour is defending seven key marginal constituency across the county, two of which – Gillingham and Rainham and Sittingbourne and Sheppey are "super-marginals" – and all are official Conservative targets.

While MPs elected on the back of Tony Blair’s historic landslide in 1997 could be on the hunt for new jobs on May 7, party chiefs insist there is all to play for despite suffering resounding defeats at last year's county council and European election.

Labour’s marginals: Chatham and Aylesford (majority 2,332); Dartford (majority 706); Dover (majority 4,941); Gillingham and Rainham (majority 254); Rochester and Strood (formerly Medway, majority 213); Thanet South (majority 664) and Sittngbourne and Sheppey (79).

The election campaign is likely to see visits by all the main party leaders to Kent along with other "big hitters" as they seek to woo support among undecided voters.

Whatever the outcome, Kent is guaranteed to have at least four new MPs.

Folkestone and Hythe MP Michael Howard, who led the Conservatives at the last election and has been MP since 1983 is standing down; as is Maidstone and Weald MP Ann Widdecombe, who was first elected in 1987.

On Labour’s side, Sittingbourne and Sheppey MP Derek Wyatt, along with Dartford’s Dr Howard Stoate and Medway's Bob Marshall-Andrews are also quitting. All were elected in 1997.

The Liberal Democrats will be hoping that disaffected Labour voters will turn to them rather than switch to the Conservatives and are expected to target Maidstone and the Weald and Folkestone and Hythe.

The election is expected to see a record number of candidates from minority and independent parties standing for election.

Read Paul's blog throughout the campaign to keep up to date with all the latest news and analysis>>>

The Green party and UKIP are both expected to field candidates in most Kent constituencies and aim to build on recent successes at the local council and European elections held in the region last year.

The BNP is also expected to put up candidates at selected seats as are the English Democrats.

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