"This is not illegal! They have withdrawn a job offer, presumably the job had a probation period and if so they should pay you in lieu of notice of whatever is stated in the contract. No contract, no case."
If you don't have a clue about the law, don't post about it.
"I employed a lady who was pregnant, she didn’t tell us until she was 13 weeks, took 52 weeks maternity and didn’t come in for any KIT days. We’re a small company, it caused hell."
If someone telling you at the same time most people do and then going on maternity leave causes 'hell' in your business, you're running it exceptionally badly!
"Why would you want her in employment? She’s dishonest for starters."
Why do you think she is dishonest? Nothing she has said on here indicates that at all. She was not at any point dishonest. In fact she was completely honest, even though she had no reason or need to be. She told them far earlier than she needed to that she was pregnant.
She didn't tell them before the interview because it is not relevant to the discussion about her skills, experience, capabilities, which were the subject of discussion, and in any case they would have had to disregard it.
I have spent the last ten years of my life working with small businesses on their HR issues, by the way. Fortunately the vast majority of small business owners aren't like you.