Speculation mounted yesterday that Barclays and HBOS would be the next banks to seek multibillion-pound cash injections, after Royal Bank of Scotland's (RBS) decision to tap the market for as much as £13 billion.

Analysts drew parallels between RBS, which has the weakest capitalistion of all European banks, and Barclays and HBOS, whose Tier 1 capital - a key measure of financial strength - is also substantially lower than rivals such as Lloyds TSB and HSBC.

Morgan Stanley analysts said that RBS's move “could trigger other raisings”, with Barclays the most likely to act next.

Alex Potter, banks analyst at Collins Stewart, said that HBOS's capital base would be eroded by Britain's house-price falls, which could force it to raise cash.

“However, with capital ratios more than a quarter better than RBS, the risks of rights issues here [at Barclays and HBOS] are massively smaller,” Mr Potter said.

Yesterday, a Barclays spokesman said that “there's been no change in our policy in respect of capital”.

Sources with knowledge of the bank, which last year lost out to RBS in a six-month takeover battle for ABN Amro, insisted that RBS's decision to raise capital did not mean that other banks would follow.

A consortium led by the Scottish bank paid €71.1 billion (£49.3 billion) for ABN.

“They've long been an outlier and they're the only ones in the UK who spent a lot of money on an acquisition last year,” a source said. HBOS declined to comment yesterday.

Bradford & Bingley, Britain's biggest buy-to-let lender, has a stronger Tier 1 ratio than RBS, Barclays and HBOS but is not as well-capitalised as other British banks.

The lender insisted this week that it was not contemplating a rights issue but analysts said yesterday that it may regret ruling out the option.

B&B was the only bank to see its share price fall after it revealed that the proportion of its borrowers behind on their mortgage payments had climbed dramatically in the past month.

The bank said that three-month arrears had risen from 1.5 per cent in March to 1.6 per cent in April - almost twice the rate at the end of December, when it was only 0.9 per cent.

Sandy Chen, banks analyst for Panmure Gordon, said that B&B's earnings could fall as a result, making it necessary to write down more of its loan book and ultimately trigger a rights issue. B&B shares fell 2p to 171p.

Tier 1 capital consists of all shareholder equity including common and preference shares. Core equity Tier 1 strips out hybrid capital, such as preference shares, while Tier 1 ratios measure the proportion of a bank's risk-weighted assets covered by its Tier 1 capital.

RBS has a Tier 1 ratio of 6.7 per cent, far below Standard Chartered, Britain's best-capitalised bank.

Under core Tier 1, RBS's capital cushion is even weaker. Morgan Stanley analysts calculate that the figure is about 4 per cent, compared with a sector average of 6.6 per cent.

Barclays' core Tier 1 is 5 per cent, 25 per cent better than that of RBS, while HBOS's is 5.7 per cent.

The Royal Bank of Scotland's acquisition of ABN Amro contributed to its low core Tier 1 ratio, which dropped from 5.1 per cent to 4.5 per cent after the bank paid £10 billion cash as part of the purchase price.

Sir Fred Goodwin, RBS's chief executive, was adamant in February that there was no problem with the bank's capital ratios.

The bank is thought to have come under pressure from regulators and the Government to shore up its capital cushion in return for assistance with liquidity through a securities-for-gilts swap being organised by the Bank of England and the Treasury.

The bank has written down £1.4 billion as a result of the credit crunch and is expected to report an even larger hit in the first quarter of this year.

James Eden, banks analyst at Exane BNP Paribas, said: “It is something of a U-turn for [Sir] Fred Goodwin.

"The fact that he has changed his mind so quickly would suggest that there has been some meddling from elements within the Tripartite Authority.”

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