Old Employer Contacting New Employer to Threaten Regarding Future Contract(s)

I recently resigned from the company I was with after some strong disagreements about the direction and architectural decisions of some senior members of staff, and started work for a new one.

During my time with the last company, particularly the last few months, I have been very critical of them both internally, and afterwards to some people outside of the company fold. Everything I have said is provably true and there has never been any implication it is not. All of the criticism is of systemic issues that led to or ignored catatrophic problems with software systems design. Something my previous company has had publicised problems with before. Nothing I said was ever personal.

After two days of my new job my current company's MD called me into his office to tell me he'd received an email. He said this was sent from a personal email address, but from someone at my previous company (from what he said the implication is someone very high up -- probably the Director of the project I last worked on, based on the details he gave, though he did not give the name). The MD told me this email said that they should be watchful I do not continue to criticise my last company publicly in future, because if I do then my new company might forfit any right to new contracts with them and might otherwise find things difficult. This email included a recent example (which took place in the short period between my leaving the last company and starting my contract with the new one) where I have criticised my former company on a publicly discoverable forum.

The Managing Director was very nice about this. He said he didn't think there was anything wrong with what I said from their perspective: that it was an expression of frustrations with my previous employer which I'd made clear to them before I took the job with them. However, he said they haven't decided yet whether they will be attempting to renew/rebuild prior relations with my old company, or to go for them commercially and to take them on, on the basis that a similar product we offer is, he believes, of higher quality (I agree with this).

Though he didn't ask me not to express myself I understood that the situation was a complex one for them. I told him, as is the truth, that I have a lot of respect for what they are doing and I don't want to complicate the landscape. Though I did not directly say I won't be criticising my former company in obvious public ways in future, and he did not ask me to, I believe there was a mutual understanding that at present it would not be politic.

Everything has been fine since and I've been settling in well and positive relations with the MD have led me to believe there is no damage. However, the whole thing leaves a bad taste in the mouth, particularly since my previous company are much larger than my current and have a lot more weight to throw around. The thing that keeps bothering me is: are there any laws or regulations that might disallow this sort of 'unofficial' economic bullying? I don't intend to challenge directly at the moment and I don't see there would be any benefit to legal action or anything like that, but I would really like to know what the law is here because something about it just seems really off.