It still exists - Loco Gauge is listed in the sectional appendix. But the modern railway has rather a lot of equipment a train must interact with correctly so it's not simply a case of physically fitting through bridges and tunnels.
Having said that, it's very possible that NR have route cleared it for a large amount of the country in one swoop by certifying it for Loco gauge, possibly even before arrival - a lot of the work can be done before the locos even got to the UK because the data is all in computer systems. Annoyingly, the PDF copies of the Sectional Appendices and PONs have vanished from NR's website for the moment so I can't check right this second if they are cleared. Somebody internal may be able to verify what clearances 93s currently have.