TORONTO - Private equity firm Onex Corp. and the Canada Pension Plan Investment Board have made a joint bid worth nearly US$4.4 billion to acquire British engineering and manufacturing company Tomkins PLC.

Tomkins said Monday it had received a tentative takeover offer worth about 2.87 billion pounds (C$4.6 billion) from the Canadian investment entities and has agreed to allow the consortium to conduct due diligence.

The proposal is one of the biggest deals ever made by Onex, a company with diversified manufacturing operations in North America and which is run by financier Gerry Schwartz. A few months ago, Schwartz said the climate for deal-making had improved, an indication the company was preparing for a major takeover.

But Tomkins said there is no certainty that a firm offer will be forthcoming.

London-based Tomkins says the consortium had made an approach to pay 325 pence per share. The company's shares were up 33 per cent to 306.1 pence in late morning trading in London.

Tomkins has two business divisions, with the primary business making systems and components for automobiles and industry, while the other handles air systems components and bathroom fixtures.

The company reported a loss of $15.5 million for the year ending Jan. 2, following a $64.6 million loss a year earlier.

Neither the CPP investment board nor Onex would answer questions about the joint bid.

"We note the announcement made by Tomkins PLC about the proposal they have received from CPPIB and Onex," said pension manager spokeswoman Linda Sims in an email to The Canadian Press.

"We have no further comment at this time."

Onex (TSX:OCX) issued a similar statement. Its shares were up 11 cents to $25.18 in early trading on Monday.

Paul Holden, a financial analyst with CIBC World Markets, says Onex's play for Tomkins would be one of its largest investments and would fit nicely into the diversified firm's portfolio.

The asset manager already owns operations in the electronics manufacturing services, aerostructures, healthcare, financial services, customer support services, metal services and other industries.

"It's not surprising ... They have the management experience and capability of running that type of business," Holden said, noting that the company has a very high success rate with acquisitions it has made in the past.

"This would be a large one for them, so I'm sure they've really done their homework and have a strategic plan in place to realize additional value out of the business," he said.

Toronto-based Onex tends to be very price sensitive, he said, adding that it must have seen an obvious way of increasing the value of Tomkins in the next five to ten years because that is the way it generally operates.

And while Onex hasn't been active in Europe historically, and most of its acquisitions are made in North America, there are deals to be had in the Old continent now, as debt crises in some European countries are wreaking havoc on the value of the British pound and the euro.

The takeover bid marks the latest in a growing number of offers this year that have been submitted by North American firms to acquire British engineering companies.

Earlier this month, URS Corp. won a bidding war to acquire U.K. transport consultancy firm Scott Wilson Group.

The CPP investment board has been on its own acquisition tear in recent months, bolstered by growth in its investment funds and the opportunity to capitalize on the lingering elements of the global financial crisis.

It has invested in infrastructure, real estate and other sectors and recently made a bid to buy an Australian toll highway operator that owns nearly a third of the profitable Highway 407 toll road north of Toronto.

Earlier this month, the board said it would spend $250 million for a piece of privately held Laricina Energy Ltd., the fund's first direct foray into northern Alberta's oilsands industry.

Meanwhile, Onex, which manages about US$12 billion of investments focused on private equity, real estate and credit securities, said in May that it is flush with cash and upbeat about acquisition opportunities.

Some of its main operating companies include electronics manufacturer Celestica, ambulance operator Emergency Medical Services Corp., aircraft parts maker Spirit Aerosystems and industrial products supplier Husky Injection Moulding,

The Toronto company's businesses generate annual revenues of $32 billion and employ 210,000 people worldwide at companies in contract manufacturing, software, aerospace and several other industrial sectors.