He can claim all he likes, that doesn't make it true.
First let's look at the shares. Your company doesn't own any shares so it can't sell any to him. The shareholders own the shares, and they won't sell any to him. The company could issue new shares and sell them, but he can't force the company to do this, and the shares wouldn't be sold to him for what I assume is a ridiculously low price, but to the highest bidder.
Next, his salary. What is actually his salary? Very often company directors get a minimal salary and hope to make money by getting paid dividends. Since you have no money, he has no right to dividends. Paying him dividends would actually be illegal. But what is his salary? You can check his contract. You can also check what salary you told HMRC about and what salary you paid PAYE for, or what you wrote onto his paychecks. Since he was a director, reporting fake numbers to HMRC would get him into a lot of legal trouble. So it's quite likely that you don't owe him any salary.
And third, his director's loan. Look at the contract. I gave my company a (tiny) director's loan, and the contract says it has to be repaid when the company can afford it. Obviously I didn't want to rip myself off :-) But this will at most give him the same rights as anyone who is owed money by the company. Actually, repaying his loan before you pay salaries (to people who are still employed), or paying for goods, could also be troublesome. You can of course avoid having money and having to repay him by adjusting everyone else's salary. And you wouldn't pay his loan back without first paying the other directors.
What he really wants is to push the risk that he took by starting a company to the other founders. There is no reason why you would allow him to do this.