One simple answer would be for T to ask for a rent reduction, backdated to their first complaint or for the downstairs landlord to take action. I don’t see why the committee would accept that the flooring is “compliant” when it quite clearly isn’t doing its job.
There are provisions under the Act for the committee to initiate its own mediation, in an effort to try to define the problem and resolve it.
Or, bearing in mind that noise is as much behavioural as it is simply structural, you could start looking at ways of requiring the upstairs people to cut the noise or face breach notices.