No, several of these are hard cut-offs. So, 103 weeks isn't two years, you can't be unfairly dismissed under the terms of this law. In this case I believe the relevant paragraph of legislation is:

"Section 94 does not apply to the dismissal of an employee unless he has been continuously employed for a period of not less than two years ending with the effective date of termination"

Section 94 is the name of a section of the current law regarding the general idea of like, employing people, and that section says you can't unfairly dismiss them, so this sub-sub clause says that only applies after two years.

Edited to add: This stuff is easier to find in the UK because although it's legalese, the Westminster Parliament is obliged by its own rules to name laws after what they do, this is an employment law so I searched for "Employment". In the US it might be called the NICEHAT Act or Jim Smith's Law or some other useless nonsense because they have no such rule.

This is the letter of the law. But I have been advised in the past that in practice, if reviewing a case, the tribunal is likely to see the accrual as gradual. So if you fire someone a week before their two years are up, they may well decide it was unfair.