Not online you can't.
when did the price change occur?
distance selling regulations suggest that it would be wiser in the eyes of the seller to accept an order at an incorrect price, that to risk complaint, investigation, and possibly prosecution.
check this here excerpt.
"Online suppliers should note, however, that incorrectly describing an item's price is likely to be
a criminal offence under section 20 of the Consumer Protection Act 1987 (CPA 1987). There are a
number of defences available, including that under section 39(1) CPA 1987: where a person took all
reasonable steps and exercised all due diligence to avoid committing the offence. (The offence can
also arise when the price was correct at the time it was placed on the web site and subsequently
becomes misleading, and therefore suppliers should ensure that systems are in place to monitor and
update prices as necessary.)
The section 39 defence is of course only available when the appropriate action is taken before the
price listed on the web site becomes misleading, and may be more difficult to make out the longer
the error is left uncorrected. However, in the absence of circumstances on which a defence could
be based, if an error is nevertheless inadvertent and rapidly corrected, this would in all
likelihood influence any decision of the Trading Standards Department on whether or not to
investigate and/or prosecute."