If the pipes originate from outside the bathroom in copper they all need bonding together with 4mm csa earth wire which should also bond the protective conductors of any equipment in the zones (i.e. shower, luminaire [electician speak for light]).
any metal pipework that does not enter from outside the zones does not have to be bonded whatsoever, otherwise we would be bonding soap dishes and ash trays.
Of course the most important part is to include a do not remove warning label, to protect future users against diy disaster plumbers.
As for the flexi pipe, if it is metal braid, even though there is a rubber washer inside it continuity should be provided by the compression fit. However let us consider the danger should it not. No danger. Only would matter if the metal braid were to be relied on to continue the bond to a metal basin, which would have to be very reare.
In a bathroom you are not at risk from stand alone metal parts, you are only at risk from parts which can introduce a potential from outside the bathroom, and from metal parts of electrical fittings (like the case of a water heater) . One of the few good reasons for bonding a boiler and it's pipework.
(I just hope that in the 17th edition they address the current malpractice of excessive boiler bonding emoticon.)