Was this already in place in the past week or so?
I do transits through the Heathrow CTR pretty frequently, maybe one a week. I did two transits last Sunday, one direct Fairoaks to WOD NDB and the other Beaconsfield-BUR NDB-Ascot-Fairoaks. Historically, it's always been SVFR in my experience.
The direct Fairoaks to WOD I received a transit clearance and NOT an SVFR clearance which confused me. I was corrected as I read back "Cleared SVFR direct WOD NDB not above 1,500'" but I was specifically corrected to a transit, not SVFR, by the ATCO.
On the other occasion, I received cleared transit Beaconsfield-BUR not above 1,500 then SVFR not above 1,000 after BUR, to maintain separation from the IFR traffic on LHR approaches/departures, and I assume that using SVFR not above 1,000' avoids the 1,000' rule.