A former Conservative MEP is to appeal against a ruling ordering him to repay £345,289 in expenses claims, saying he wants to "clear his name".
Den Dover said he submitted the claims, which the European Parliament argue were unjustified, in "good faith" and that the rules were "far from clear".
But Lib Dem MEP Chris Davies has urged the police to investigate whether Mr Dover committed a criminal offence.
Mr Dover was expelled from the Tory Party in 2008 for "gross misconduct".
Mr Dover, who represented the North West of England in Brussels until 2009 and is a former MP for Chorley in Lancashire, originally faced a demand to repay £538,000.
The European Court of Justice reduced that amount by just over £192,000 on appeal, saying the parliamentary authorities had not sufficiently demonstrated all the claims were unjustified.
Announcing his intention to appeal against the ECJ verdict, Mr Dover said he did not believe he should be compelled to repay anything as the judgement required MEPs to "retrospectively" produce records to verify claims dating back many years.
"Had I known of this requirement at the time the expenses were incurred, then records would have been kept," he said.
Mr Dover said he was taking legal advice and would "continue to fight to clear my name".
"As I believe is clear from the judgement, and from the evidence submitted before the court, the rules regarding the payment of expenses and allowances to MEPs at the time were far from clear," he said.
"I submitted claims in good faith in accordance with the relevant rules as I, and other MEPs, understood at the time."
The European Parliament launched a probe in 2008 after it emerged Mr Dover had paid nearly £1m to a company, MP Holdings, which included his wife and daughters among its directors. The money came from allowances MEPs receive to pay staff salaries and costs.
It ruled that only £421,156 could be justified in salaries, National Insurance and legitimate staff travel expenses - and the remainder was "without justification".
Mr Dover told the court it was up to the parliament to prove the payments were unjustified, pointing out in court submissions that "the requirement to provide documentation justifying each item of expenditure since 1999 did not exist when the relevant expenses were incurred".
But Mr Davies, MEP for North West England, said further action should be taken against the former MEP.
"I am calling on the police here to investigate whether Mr Dover's actions were fraudulent and warrant criminal prosecution," he said.
"Most MEPs know the difference between right and wrong when spending public money but Mr Dover treated the European Parliament like a private piggy bank and let greed overtake honour.
"The Parliament has been shamefully weak in the past and has too often turned a blind eye to abuses but it is now demonstrating that such behaviour will no longer be tolerated."