Brendon Hartley is to replace British driver Jon Lancaster in the #24 Ocean Racing Technology car alongside Nigel Melkur, it emerged late on Thursday evening.

"Racing GP2 in Bahrain with Ocean Racing Technology!", tweeted the 22-year-old Kiwi driver. "Very very last minute, am still a little surprised to be here. Let's go racing!"

Hartley competed for Ocean Racing in the last two rounds of the 2011 GP2 Series as a replacement for Kevin Mirocha, having made his d?but in the series in the last two rounds the previous year with Scuderia Coloni filling in for the injured Vladimir Arabadzhiev. He had also been an official reserve driver for both Red Bull Racing and Scuderia Toro Rosso as a former longtime member of the Red Bull Junior Team.

The late change is rather unusual, with Ocean Racing's pre-race weekend press release issued on Wednesday referring to Jon Lancaster's involvement in this weekend's Bahrain feature and sprint races.

"We did some good tests in the simulator and I am sure that they will be essential going into the race weekend," the press release quoted Lancaster as saying. "I think that we will be more competitive here than in Malaysia."

But later that same day, Brendon Hartley tweeted that there as a "Chance I may be racing this weekend!" and then adding: "On my way to London Heathrow airport ... Any guesses on where I'm heading?" before subsequently revealing that he had landed in Bahrain and was on his way for an urgent seat fitting.

There was no update from Lancaster's Twitter stream or official website regarding the reason for the late change, or any official word from Ocean Racing Technology's own media channels regarding the change. It's not clear whether the change is just for this weekend or for both Bahrain race weekends - or is a potential longer-term arrangement.

Lancaster had made his GP2 d?but the previous month in the season opener at Sepang in Malaysia as a relatively short-notice signing to the Portuguese team. However, he retired very early in the feature race with technical issues after qualifying in 21st, and only managed to fight back to 17th place in the following day's sprint event.

However, it's not know whether the change of drivers this week is related to the performance in Malaysia, or to driver illness, issues relating to sponsorship backing, the current unease about the political situation in Bahrain - or another as-yet unidentified cause.

Earlier this week, the Barwa Addax team also made an unexpected driver change when they announced that veteran Spanish GP2 driver Dani Clos was to replace Czech driver Josef Kral at this weekend's races, alongside Venezuelan driver Johnny Cecotto Jr.

The Addax team's subsequent official pre-Bahrain press release confirmed the switch from Kral to Clos, but still gave no reason for the change of drivers nor did it indicate whether the replacement was a one-off deal or likely to continue into subsequent race weekends.

GP2 action starts on Friday morning at 9.55am with the practice session following F1 Free Practice 1. The qualifying session follows FP2 at 1.55pm, with the feature race 1 on Saturday afternoon at 1.40pm and the sprint race 2 on Sunday afternoon at 8.35am. Coverage of all sessions is carried live in the UK on Sky Sports F1.