Hello both,
thanks for your thoughts.
You're absolutely right - the raw data (i.e. the time-stamp) received from each satellite is processed by the receiver and it then generates the NMEA sentences which include, amongst a load of other things, the calculated fix. You may be right that the timestamp itself is not made available via any of the NMEA sentences, but I haven't been able to find anything that definitively says that.
The data sheet for the GPS (it's a Neo-6m, but I don't think the specific RX module matters, as NMEA is a general standard) just says it uses the "standard NMEA messages", but none of them return the timestamp data on a per-satellite basis.
Thanks 