The long and bitter dispute between Express Dairies and Robert Wiseman over anti-competitive behaviour in the Scottish milk market is set to run on.

In another twist this week Express has challenged the Office of Fair Trading’s decision to draw a line under its inquiries into the saga.

The first inquiry, into Wiseman’s alleged abuse of a dominant market position, was closed in August after the OFT felt there was insufficient evidence to proceed.

The second, into alleged cartel activity, was closed on Wednesday.

However, Express is appealing the first decision and seeking legal advice on the second.

A spokesman said the OFT’s admission that it had grounds for suspecting an infringement of the Competition Act made its decision to close the inquiry "irrational". Calling it quits sent a "clear message to cartels that if discipline is maintained the OFT may not continue to pursue investigations," he added.

Wiseman said it was astonished Express was prepared to commit even more time and money into pursuing allegations that the OFT had failed to substantiate after 18 months of investigations. While Express clearly felt the issue hadn’t been resolved, said a spokesman, the OFT’s decision to close the inquiry clearly equated to a "‘not guilty’ verdict in any other language".