This is something I haven't seen before! Although there are both up and down relief lines between Challow and Wantage Road, 66522 is seen here passing Grove on 13 January 2023 with the 4L36 07:39 Wentloog to Felixstowe North freightliner, running in the up direction on the down main line! It had just been overtaken by the 1A15 10:00 Bristol Temple Meads to Paddington GWR IET. The liner was running 47 minutes late, due to being routed via Bath, as its normal route was closed due to flooding near Chipping Sodbury. Although of course this section of line has bi-directional signalling, the normal move would be to have this train use the up relief line.