Essex 395 (Lawrence 147, ten Doeschate 103, Harmer 50*) beat Surrey 174 (Porter 5-62, Cook 5-53) and 181 (Harmer 7-58) by an innings and 40 runs

Simon Harmer remains Essex's matchwinner in what has become county cricket's most predictable plot. Just as in a Hollywood movie, the couple who dislike each other are certain to fall in love, so Harmer is certain to roll over any opposition who turn up to Chelmsford.

There was a slight twist in his wicketless first innings against Surrey, but normal service was resumed as he took 7 for 58 on a surface where Amar Virdi, the most promising young English offspinner in the country, barely got a ball off straight in returning 3 for 116 in 32.1 overs. That's 78 for the season at 18.11 for Harmer with five or more in an innings on nine occasions.

It was two minutes to six on the third evening by the time Surrey were dispensed with by an innings and 40 runs and with that came a historic moment. Essex have won every home Championship match this season - something they have never previously achieved - with only two of their seven matches, against Warwickshire and Kent, reaching the final day.

From the moment that news filtered through of Somerset's defeat at the Ageas Bowl, Essex knew that much now lies in their favour as they await their Championship decider at Taunton next week.

That match is no longer quite winner-takes-all. Essex's 12-point buffer means that if they avoid defeat next week it would be sufficient to secure their second title in three years. Somerset, by contrast must win and (barring a freakish division of bonus points) that would be enough to give them the title for the first time.

Ryan ten Doeschate, his captain, praised how pressure brings out the best in Harmer and he will hope that reputation lasts one more week. It will need to because, as ten Doeschate observed, the summer has been one of "two counties playing with high intensity throughout".

"One of Simon's biggest attributes is that he stands up when he's needed," ten Doeschate said. "He thrives on these occasions. He wants to play in the big game and he makes things happen with the ball. Today again underlines the sort of player he is. He turned our innings into a match-winning, unassailable lead and then follow it up with the ball. He's a special cricketer."

When Hampshire beat Somerset at the Ageas Bowl, and Kyle Abbott completed one of the greatest statistical performances in Championship history, Surrey were in disarray at 115 for 7, facing a first-innings deficit of 221. But nearly two hours elapsed before Essex completed the job. Fittingly, Harmer had the last act, virtually yorking Morne Morkel as he tried to loft him down the ground. He found reasonable amounts of turn and bounce and varied his pace aggressively, but ask who has played him wonderfully well this summer and barely a name is forthcoming.

"Beat Surrey and then let the rain commence," was how one observer summed up news of Somerset's defeat. In Chelmsford, they will now happily imagine that this week's sunny weather is about to break and a deluge is already heading to the south-west. That is not yet evident. The latest Met Office forecasts predict only occasional showers over the first two days.

Instructions had gone out from the Essex coaching staff not to divulge the glad tidings of Somerset's defeat over the PA system. Essex's players supposedly had to remain oblivious to the result, even though the county's Twitter account engaged in some joshing with Abbott. Presumably, mobile phone signals were also blocked all over Chelmsford in case a spectator had a word at third man, the media would have been arrested by a steward if they tried to leave the box and carrier pigeons were being gunned down over the River Can.

If it was meant to keep Essex's minds on the job in hand, it didn't exactly work. Liam Plunkett soon became the eighth batsman to fall, only for Jordan Clark and Morkel to embark upon an unexpected, and pretty pointless rearguard action which brought 43 in 18 overs against semi-defensive fields as Surrey, basking on a glorious September evening, and with the realisation that there may not be many more to come. seemed to want the game to last forever.

Surrey needed a quick kill at start of play with Essex 128 ahead with four wickets remaining. Instead. Harmer prepared the ground for his own spell with a rapid pre-lunch fifty and ten Doeschate also completed a century largely fashioned on the previous day.

With their fate as good as sealed, Surrey's second-innings response was lacklustre as they failed to log a half-century in the match. Harmer had Mark Stoneman lbw in his third over and Scott Borthwick soon followed, attempting to pull over midwicket but getting a leading edge and popping up a simple catch for Nick Browne at short cover.

Jamie Smith has looked full of promise and had the audacity to lift Harmer for six over long leg, but he instantly knew his fate as a quicker ball rapped him on the pads. Ollie Pope sped to 30 before pulling to Aaron Beard at midwicket. The next ball represented Surrey's nadir as he tossed up a ball outside off-stump and Will Jacks, with an act of irresponsibility that suggested one-day cricket is a canker in his four-day game, attempted a fulsome drive at his first ball and was bowled through a sizeable gate.