Once more unto the breach is the rallying call at BHP Billion today. The world's biggest mining group is marshalling its resources for one last push at the Rio Tinto boardroom door. However BHP's campaign message lacks the killer blow that Rio Tinto shareholders are looking for — an increase in the headline value of BHP's proposed £67 billion offer for Rio.

As a result Rio's shares fell as investors expressed their disappointment at BHP's failure to raise its offer, a month after being comprehensively rejected.

BHP has resorted to the tactics of trying to demonstrate that it is a better company than Rio — always a weak basis for a takeover battle. In this instance the figures released today appear to support BHP's claim that it pays to look at relative, rather than absolute value when weighing up this proposed merger.

BHP boasts 37 per cent compound annual growth rate since 2001, compared to Rio's 29 per cent. Its production growth of 8 per cent a year, is double that of Rio's. Its investment in organic growth projects has also been more than double that of its rivals. These figures make attractive reading but BHP neglects to point out that much of its growth is due to its oil assets and that it is much harder to achieve growth in mining.

BHP may also have unwittingly made another stick for its back with today's spin. Optimistic Rio shareholders will see behind them an implicit suggestion that the $3.7 billion cost savings promised by BHP could be even higher. Also, the larger company has made a very good case for why it should be paying more.

Rio Tinto shareholders have shown no appetite to discuss a one for three share offer. The pressure is very much on BHP to improve its terms and yet it has failed to do so, despite the fact that since Rio asked the Takeover Panel to police the approach the clock is very much ticking.

With no serious rival to BHP around, the Australian group's disinclination to raise its initial offer is understandable. However, the Rio chief Tom Albanese's jibe last week that BHP's bid looks "dead in the water" rings even more true today with this disappointing statement

Times Recommends

• Lies and cover-up at MG Rover exposed by report
• High oil prices push manufacturing costs up
• Primark founder steps down as chief executive