The five key seats in the county home of Essex Man and Mondeo Man

"Essex Man" went for Margaret Thatcher, "Mondeo Man" for Tony Blair but is the 2015 equivalent more likely to vote for UKIP?

Not so long ago, just one Essex seat mesmerised the British political class.

That seat was Basildon, the spiritual home of "Essex Man" and time-proven bellwether of political meteorology.

The rule was simple: win Basildon, form the next government. It had been that way since 1974.

Lured by a range of policies such as "right to buy", blue-collared Essex Man flocked to Thatcher in the 1980s. With his support, she won again and again.

Nigel Farage out on the election trail in South Ockendon

The importance of Essex Man was not lost on Tony Blair, who, during the 1990s, heralded the age of "Mondeo Man", the self-employed working man with a new mid-range motor car on the driveway.

But Basildon - the constituency - is no more after boundary changes in 2010. South Basildon and East Thurrock perhaps best represents the old seat, though UKIP is now firmly in the running there, and elsewhere.

There are now five key seats to watch in Essex during the early hours of 8 May.

Each could give clue as to who will be sitting on the government side of the green benches of Westminster:

Thurrock

Polly Billington has been joined by celebrities on the campaign trail including Eddie Izzard on Grays High Street

This is UK target seat number two for Labour. The Conservatives' Jackie Doyle-Price won by just 92 votes in 2010, only the second time the Tories have won Thurrock in the past 40 years (the Conservatives won in 1987).

Labour has a high-profile candidate in former Ed Miliband adviser and BBC journalist Polly Billington. This industrial South Essex constituency, which borders London and is split by the M25, has become an three-way ultra-marginal.

UKIP has entered the fray, and in the last constituency poll carried out by Lord Ashcroft in July 2014, its candidate Tim Aker led on 36%, with Labour on 30% and the Conservatives on 28%. All three parties are pumping resources into Thurrock and have been campaigning full-time since January.

Conservative cabinet ministers from Theresa May to George Osborne and Labour-supporting celebrities like Brian May and Eddie Izzard have joined the candidates campaigning. Nigel Farage addressed an audience of more than 1,000 local people last month - the largest public political rally seen in Essex in years.

The stakes couldn't be higher, and the tension between the three, when in the same room before a local BBC Essex debate, palpable.

A full list of candidates for Thurrock can be found here.

Castle Point

In Castle Point, the Conservative election bus has periodically been tailed by the UKIP white van

This is a fascinating seat. It has the fifth-highest level of home ownership in England and very high employment levels - one in 10 work in finance and insurance. Around South Benfleet there are homes that would not look out of place in Beverly Hills.

But there is also a large proportion of construction and blue-collar workers, a very low number of ethnic minorities and a below-average university- educated population. This demographic mix has, in the last two years, has seen a meteoric rise of UKIP support with one recent local poll putting the party one point behind the Conservatives.

Mr Farage chose Canvey Island to launch UKIP's election campaign in February. The Conservatives are confident they can keep the seat and have an experienced team backing-up Rebecca Harris for a second term. But UKIP has an energetic and charismatic candidate in Jamie Huntman who could cause one of the biggest Conservative upsets of the night.

A full list of candidates for Castle Point can be found here.

Colchester

Sir Bob Russell (bottom right) with party leader Nick Clegg in Colchester

In 1997, this was a new three-way marginal which the Liberal Democrats won. Five elections on, the north Essex garrison town has become a Lib Dem safe seat and candidate Sir Bob Russell is defending a 7,000 majority.

Conservative candidate Will Quince is standing for a second time and has had many high-profile Tories campaigning with him. This is one of the 23 seats the Tories say they need to win to form a majority government.

On his second visit to Colchester in as many months, Lib Dem leader Nick Clegg accused the Conservatives of trying to buy the election here by using campaign money from hedge-funders. Mr Quince says he is spending within the rules.

The Lib Dems are incredibly well-organised in Colchester and run the council with Labour. You still see as many, if not more, of their banners outside houses than for any other party. If the Lib Dems lose Colchester they are in very serious trouble.

A full list of candidates for Colchester can be found here.

Harlow

Robert Halfon has been out on the sides of main roads around Harlow campaigning in front of commuters early in the mornings

Labour needs to win this seat to form a majority government. In 2012, it took control of the council from the Conservatives and unemployment in Harlow, a largely working-class town, remains above the national average.

Around the shopping precinct, a lot of people have told me they wouldn't vote Conservative or for David Cameron. But when you mention Robert Halfon, the Conservative candidate, most think he has been good for the town.

Mr Halfon successfully campaigned to cut fuel duty and the prime minister is said to have called him "the most expensive MP in Parliament". UKIP has picked up his policy to cut NHS car parking charges for their manifesto.

All this makes Labour candidate Suzy Stride's task much harder. Labour seems to be focusing more resources on Thurrock than Harlow. An Ashcroft poll gave Mr Halfon a 10-point lead over Labour. If this is the result on 7 May it will be an impressive Conservative hold in a marginal seat.

A full list of candidates for Harlow can be found here.

South Basildon and East Thurrock

Calm before the storm: the candidates fighting for South Basildon and East Thurrock

This is the seat that most closely represents the old infamous national bellwether. UKIP had high hopes after significant local council gains, but has problems including a saga over their candidate selection process in December.

The Conservatives are quietly confident that Stephen Metcalfe will hold the seat.

But Labour tells me locally it is gaining momentum and that from local canvassing it has moved back into second place ahead of UKIP. South Basildon and East Thurrock could still be the bellwether between the two largest parties in 2015.

A full list of candidates for South Basildon and East Thurrock can be found here.