Not unaware of the law
If you read the judgement you'll see that Capita was not unaware of the law and in fact offered him Shared Parental Leave. But on statutory shared parental pay.
The problem was that female employees who came over from Telefonica (under TUPE) could take 14 weeks' maternity leave on full pay. Male employees from Telefonica could take two weeks' paternity leave on full pay. In this case the medical advice given to the employee and his wife was that the wife should return to work (after the two weeks' compulsory maternity leave). The employee asked to take the 12 weeks' leave on full pay to care for the baby, which would have been no problem if he were female.
Capita argued that the entire 14 weeks' paid leave was to do with recovering from childbirth and so, as he had not given birth, the employee was not entitled to it. The tribunal found Capita's refusal to be direct discrimination because only the first two weeks (compulsory maternity leave) is directly to do with the birth. The remaining 12 weeks' leave was to care for the new baby, which could equally be done by either parent.
Capita then appears to have very poorly handled his grievance, caused him a lot of stress for which the doctor signed him off sick, and then tried to manage him out of the business when he returned to work.