* Melrose offers to bolster GKN pension scheme
* Dana to offer secondary London listing with its deal
* GKN investors must choose takeover or break-up
* Dana upgrades outlook (Adds shareholder comment)
LONDON, March 19 (Reuters) - The battle for British engineering company GKN intensified on Monday, with both Melrose and Dana sweetening their proposals before a March 29 takeover deadline.
Melrose offered to inject about 1 billion pounds ($1.4 billion) into GKN's pension scheme in its latest attempt to convince shareholders to back its 7.8 billion pound hostile bid and win over political opponents of the deal.
It also lowered the acceptance condition for its offer to 50 percent plus one share from 90 percent, increasing its chances of winning the company after investors appeared divided on the matter.
GKN is trying to fight off the Melrose bid with an alternative $6.1 billion deal to merge its automotive business with U.S. company Dana Incorporated, leaving GKN focused on its aerospace division.
GKN shareholder Columbia Threadneedle on Monday threw its weight behind GKN's plan and said it planned to reject the Melrose offer, becoming the biggest investor yet to make its position known.
Dana said on Monday it would seek a secondary listing in London, a move which should enable more UK shareholders to back the rival plan as some funds are subject to rules which prevent them from holding U.S. stock.
The U.S. company also promised GKN investors a slice of its dividend as it said it would pay its current quarterly dividend of $0.10 per share to the enlarged shareholder base.
The plan for a secondary listing came after Dana executives had met GKN shareholders.
"The clear message from shareholders is that they want to be able to hold stock in a combined Dana plc," Dana said in its statement.
Aiming to give GKN shareholders extra confidence in the future of the merged GKN-Dana unit, the U.S. company on Monday also upgraded its margin and sales guidance, saying that it had "over-achieved" on synergies from past acquisitions.
GKN's shares were down 0.2 percent at 426.5 pence at 1348 GMT, while Melrose shares were down 0.5 percent at 223 pence.
Jefferies analyst Sandy Morris said GKN shareholders were in a fortunate position as, in his view, none of the options "look bad". He added that breaking up GKN's auto and aero units would make valuation easier.
"There remain some imponderables such as the risk of Melrose morphing into GKN. The market struggled to understand and measure GKN as currently comprised and could do so again if Melrose owns GKN for 3-5 years," he said in a note.
The formal proposal from Melrose to GKN's pension scheme trustees to inject 1 billion pounds into the funds over the Melrose ownership period represented a huge increase on its previous plan to add 150 million pounds.
Some British politicians have objected to Melrose's bid, citing worries that GKN's pension scheme would be weaker under new ownership, and risks to national security as GKN is a supplier of parts to the Eurofighter Typhoon.
The fate of deficit-ridden pension schemes after company takeovers is a concern in Britain following the collapse of department store chain BHS in 2016. Melrose said that its new proposal should alleviate those concerns.
"The proposal...is a clear example of what Melrose does which is good for pensioners and shareholders alike and shows we are a good custodian for all stakeholders," Melrose said in its statement.
Melrose said the pension offer exceeded GKN's deficit reduction package of 528 million pounds which it had agreed with the trustees alongside the Dana deal.
The length of Melrose's ownership period is unclear, however. As a turnaround specialist, its business model is typically to break up companies once it has improved their performance.
GKN shareholders are left to choose between the two options: Melrose's offer of 81 pence in cash for each GKN share plus 1.69 new Melrose shares, a deal that will hand them a 60 percent stake in the London-listed turnaround specialist.
Or they can back GKN's plan, which would see them take a 47.25 percent stake in New York-listed Dana, and accept a promised return of 2.5 billion pounds from the planned sale of its powder metallurgy business and the Dana deal.
Melrose's hostile bid has so far split GKN shareholders. Columbia Threadneedle, a top 10 shareholder in GKN with a 3.4 percent stake according to Reuters data, said on Monday it would reject the offer, joining top 30 investor Jupiter Asset Management's Steve Davies. While Aviva Investors, also in the top 30, has lent support to the Melrose deal.
Airbus, GKN's biggest customer, has also been vocal. It said on Thursday it could not guarantee new work to an owner with a short-term perspective. Some commentators see Melrose as operating with a short-term model. ($1 = 0.7179 pounds) (Reporting by Sarah Young; editing by Adrian Croft)