On RTT it is called Westboune Park CS
https://www.realtimetrains.co.uk/search/detailed/gb-nr:WBRNPKS?stp=WVS&show=all&order=actual
Looking at Google Maps it seems to be about 2000 ft from Portobello junction
Many thanks Kevin.
I hope you don't find this too pernickety, but ..... I had, rather simplistically, assumed that Westbourne Park Junction would refer to the physical pointwork connecting the main line with the tracks leading to crossrail. Whereas, from your response, perhaps it's being used to refer to the NR/TfL boundary, located in the vicinity of the Westbourne Park turnback sidings - referred to in RTT as Westbourne Park Cs. Is that what you meant?
And I had understood crossrail to start at its junction with the main line, but it's clearly more accurate to state that crossrail starts at the NR/TfL boundary - which is why I'm using the rather clumsy phrase 'tracks leading to crossrail' for the tracks leading from the NR/TfL boundary to the junction with the main line.
What I was really wanted to know was the distance (miles and chains) between London Paddington (low level) and the junction of the main line with the tracks leading to crossrail, perhaps mistakenly using the term Westbourne Park Junction to refer to the junction itself. I've done some further digging (see below), and I think I'll use Portobello Junction (London) as the actual junction of the main line and the tracks leading to crossrail, and for determining related distances - unless anyone can suggest something better!
I'd seen Westbourne Park Cs in RTT prior to posting my initial question, but given its 'Cs' suffix, which usually indicates Carriage sidings(s), I had thought that this refers to the Westbourne Park turnback sidings, rather than the Westbourne Park Junction (which I had understood would refer to the actual junction between main line and the tracks leading to crossrail). Most junctions between lines are indicated by a Jn suffix in both RTT and Railmiles, and I had expected the junction (ie pointwork) between the main line and the tracks leading to crossrail also to be indicated with the 'Jn' suffix, rather than with the 'Cs' suffix. Hence my initial question.
The relevant map in Trackatlas (3rd edition), p108, shows the 'Crossrail datum 0.0km' 0m 78ch Main Line, which indicates the NR/TfL boundary, to be where the turnback sidings are located. But the map in Trackatlas and the satellite view on Google maps show the physical pointwork connecting the main line to the tracks leading to crossrail to be further west - more or less where Portobello Junction is located.
Railmailes gives the distance between Portobello Jn (London) PRTOBJP and Westbourne Park Cs WBRNPKS as 0m 19ch, and between Westbourne Park Cs WBRNPKS and Paddington Crossrail PADTLL as 1m 4ch - which is the same mileage RTT shows for trains using the Westbourne Park turnback sidings. Incidentally Railmiles also shows the mileage between London Paddington PADTON and Westbourne Park Cs WBRNPKS to be 1m 47ch, the route being London Paddington, Royal Oak Junction, Portobello Jn (London), Westbourne Park Cs - which would seem to confirm that the actual junction between the main line and the tracks leading to crossrail is at Portobello junction.
Thanks for your help