And John Pickersgill, Revenues Programme Manager with International Computers Ltd (ICL), said he believed the council itself should bear its own losses.
St Albans is suing ICL for compensation over 'defective' COMCIS software which the company installed in 1989 to deal with the changeover from rates to poll tax.
ICL admits there was a fault which resulted in inaccurate figures for the number of adult community charge-payers in the council's area being presented to the environment secretary.
The ministry 'would not or could not' help the council out of its predicament, the court heard.
And, as a result of the computer under-stating the number of adult poll tax-payers by about 3,000, the council claims it lost almost £1.2m in revenue that financial year.
The court heard ICL denies liability to cover the losses, the extent of which are also in dispute.
And, as a back-stop, the company relies on a clause in its contract with St Albans limiting its liability to £100,000.
The council insists that the limitation clause is unreasonable and unenforceable in all the circumstances of the case.
In the witness box today, Mr Pickersgill said that the council had been informed that the software package was not without faults.
The figures put out by the computer should have been manually checked before submission to the environment secretary, he told the court.
St Albans claims that ICL representative, Michael Turton, told them that the computer generated figures could be safely relied upon.
Richard Mawrey QC, for the council, put to Mr Pickersgill: 'Are you saying that the council representatives should have ignored him or disbelieved him.'
He replied: 'I am saying that the figures should have been validated. Mr Turton may well have given the best advice at the time.
'The council had evidence themselves that the computer process was in error when the output of the accounts scan produced errors. They should have taken it as an indication.'
Mr Mawrey asked: 'Why, if the council has suffered a £1.2m loss, should £1.1m of that fall on the chargepayers of St Albans?'
Mr Pickersgill said: 'ICL say that we advised St Albans DC, as we advised others, that there were errors in the software.
'It was the responsibility of the community charge register officer to make the very best estimate of the relevant population.'
Mr Mawrey said it was ICL's case that St Albans could and should have checked the accuracy of the computer figures.
He asked: 'If the judge comes to the view that the council could not reasonably have rectified the effects of the error, why should the St Albans ratepayers pay and not ICL?'
Mr Pickersgill replied: 'In December 1989, ICL had advised its users that there were errors in the software and it was the responsibility of the community charge register officer in the authority to make the very best estimate.
'They (the council officers) should have done that on the understanding that the software supplied to them could not be relied on.
'I cannot believe that ICL could be held at fault in this,' he told the court.
Mr Pickersgill said St Albans DC was 'well aware' of the terms and conditions of its contract with ICL, which limited the company's liability to £100,000.
Mr Mawrey asked: 'You are saying that people who buy defective software are just unlucky and should stand the losses themselves.'
He replied: 'I am not saying that.'
Mr Pickersgill told the court that ICL was the market leader in revenue systems computing, suppling 121 of Britain's 405 local authorities, and had an 'excellent track record'.