Shares in Hanson almost hit the £7 mark this week for the first time in a decade as the materials giant's decreasing asbestos liabilities left it wide open to a takeover approach.

Shares in the FTSE 100 company rose about 3.5% to 692.5p at the end of last week on the back of takeover speculation, which has led to steadily rising figures over the past year (see graph).

Murray: Likely to ward off bidders

Murray: Likely to ward off bidders

Hanson is considered ripe for takeover because all the other large British heavy materials companies - Tarmac, Blue Circle, RMC and Aggregate Industries - have already been snapped up by international conglomerates.

Hanson is the last to remain independent but its asbestos liabilities were considered large enough to put off possible bidders, who would also be likely to get a hostile reception from Hanson chief executive Alan Murray and the rest of the board.

On Monday, Hanson said one of its US subsidiaries, responsible for about 20% of the group's £34m-a-year asbestos costs, had reached a settlement with its insurers.

Under the settlement, Hanson has agreed to pay the first £20m of its future asbestos costs over three years, after which it has secured insurance cover for an amount that is expected to last "well beyond 2020".

However, Hanson was dealt a blow on Tuesday when the US Senate voted against the creation of a federal compensation fund for asbestos sufferers, which would have limited Hanson's liabilities.

David Taylor, analyst at Teather & Greenwood, said: "The bill has been in the legislative long grass for a while and one must assume a low probability of success has been priced in. Hanson's own view has been consistently cautious."

There was speculation last week that Hanson was being eyed closely by French materials giant Lafarge. However, some City sources said this was less likely after Lafarge announced last week that it had made a $3bn (£1.7bn) cash offer to buy out minority shareholders in its North American subsidiary.

One source said a deal between the two companies would result in too much of an overlap, both regionally in the UK and especially in the USA.

Other possible interested parties could include Holcim, CRH, US companies such as Martin Marietta and financial buyers such as venture capitalists or a banks.

Hanson declined to comment on the takeover speculation.