Poulter hit a one-under-par 71 to move top of the leaderboard alongside compatriot Callum Shinkwin and Australian Andrew Dodt on nine under par.
Another Englishman, Andrew Sullivan, was on seven under, one shot clear of Sweden's Johan Carlsson, Ireland's Paul Dunne and New Zealand's Ryan Fox.
Only five shots separated the top 17 players after a difficult day in which driving wind and rain made for extremely testing conditions.
"The 12th was tough as I have seen in terms of wind and rain. They were brutally tough conditions," Poulter said. "I just had to hang in there pretty strong."
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Joint overnight leader Padraig Harrington of Ireland was the main casualty with a 79, including six bogeys and a double-bogey, which dropped him back to two under.
Northern Ireland's Graeme McDowell produced an eight-birdie 68 to move into contention at five under.
For those players who have not qualified for next week's British Open at Royal Birkdale, three places are available with a top-10 finish.
(Reporting by Neil Robinson, editing by Ed Osmond)
