BERLIN: Volkswagen and Porsche could push through their planned merger next year and overtake Toyota to become the world's biggest car company by 2018, VW's financial director was quoted as saying on Monday.

"If everything goes smoothly economically, or the situation on the financial markets is particularly favourable, we could put our foot down and merge the two companies in 2010," Hans-Dieter Poetsch told Die Welt daily.

"This is of course a very optimistic scenario," he added.

When Volkswagen, Europe's biggest carmaker, and luxury brand Porsche sealed the deal on the merger Thursday -- ending a four-year battle marked by family feuds and boardroom battles -- the goal was to complete the tie-up by 2011.

Under the terms of the agreement, Volkswagen will initially buy a 42-percent stake in debt-laden Porsche by the end of this year for 3.3 billion euros (4.7 billion dollars).

In another arrangement intended to ease the takeover, the Gulf state of Qatar is poised to take a 10-percent stake in Porsche and acquire the majority of stock options the sportscar maker holds in VW.

Poetsch also said in the interview that the combined company could overtake Toyota to become the world's largest auto firm by 2018 at the latest.

"I think we could even achieve this goal a little bit earlier. The reason it is not going quicker is because we are not strong enough in the US," he said.