Yes, the hub is identical
Same 4x95.25 PCD and same 57.1 mm centre bore: wheels from Rover 100-Serie bolt on and centre on Triumph TR8 without rings. You still need to check the offset and tyres, detailed below.
≈: width estimated from the original tyre size.
Wheel by wheel: offset and tyres
Each original wheel from Rover 100-Serie is compared with the one from Triumph TR8 of the same diameter: how much closer the wheel gets to the shock absorber or how far it sticks out of the wheel arch, and whether the tyre keeps the same overall diameter.
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≈5Jx13 ET52 · 155/65R13 — Check on the car
Compared with the original ≈6Jx13 ET25 on Triumph TR8: shock absorber side +14.3 mm, wheel arch side −39.7 mm, tyre diameter −9.8 % : fit it with the original tyre size of Triumph TR8 (185/70R13), not that of Rover 100-Serie.
Comparison for guidance only (estimated width). Check in detail
Before fitting the wheels
An identical hub is not enough: offset, width and diameter change the position of the wheel, and larger calipers can touch a smaller wheel. Original wheels often use bolts or nuts with a specific seat: keep the fixings intended for the wheel, with the thread of Triumph TR8 (Ecrous - 12x1.50), tightened to the torque shown on its vehicle page. Finally, check that the size is among the approved fitments for your vehicle. This comparison is for guidance only: have the fitting approved by a professional.
And the other way round: wheels from Triumph TR8 on Rover 100-Serie?