What is the nature of the load you say FLC is 22amps but is it possible for it to overload under fault senerio, i assume your trying to argue regs 433.1.1 against 433.3.1 or vice versa?
E.g. If you had a DOL motor with a 22amp flc then it will have an overload device set at 22amps if not lower depending on the nature of its job, in this senerio you can argue the load cannot exceed 22amp and thus a cable large enough for this load but undersized to the front MCB could be used, as long as it give adequate short circuit protection and you also comply to section 434.
I wouldn't ever use this regulation as routine practice as a change in the nature of load attached etc may render the circuit without adequate overload protection of the cable where-as if it was originally sized so 'In' is not less than 'Ib' then it can fall back on it, simple things like repairs or uprades to the load could leave this regulation exposed and this is why i would never use it intentionally to cut costs.
In your case your misinterpreting the direction of this reg' and no you cant as it a socket outlet and loading is variable to the freedom to plug anything into it so yes 20amp will comply assuming rcd protection is also in place, If these are large commercial servers you got alot more to worry about with compliance than your query like functional earth requirements etc, if just standard office servers that sit under a desk you sould be fine.
If it's XLPE insulated (which seems to be the standard offering nowadays) then the current carrying capacity is 36A single phase clipped direct (table 4E4A), so no problem. You might have to take the higher conductor operating temperature into account at the terminations though.
You quoted your senerio as a twin socket thus to comply then rcd protection required, you can get around this because you are using swa but the outlet cant be a standard 13 amp socket and would need to be a dedicated isolater of some nature. There are exceptions to the rule but i doubt this is a socket dedicated to feeding a kidney dialysis machine also if not domestic it can be classed as under the supervision of an instructed person and rcd protection is not required, lack of info means we cant make a call on your situe but regs apply either way and you need to cover your back in the event of a future accident.