Director and inter company loans

I have a client who has taken large sums out of one of his companies and then put most of this in to fund another company he owns. We treated the original withdrawals as overdrawn director loan account with S.419 tax potentially due soon.
My client argues it is really an inter company loan which will be repaid and there shouldn't be a problem but as the money has been outstanding for about nine months and also it did not arise from trading transactions I don't believe we can treat as a simple inter company balance. He is prepared to pay interest from one company to the other if this helps the situation.
I'm not convinced but would welcome comments.