Yes, the hub is identical
Same 4x95.25 PCD and same 57.1 mm centre bore: wheels from Triumph TR8 bolt on and centre on Rover 100-Serie 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 Triumph TR8 is compared with the one from Rover 100-Serie 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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≈6Jx13 ET25 · 185/70R13 — Check on the car
Compared with the original ≈5Jx13 ET52 on Rover 100-Serie: shock absorber side −14.3 mm, wheel arch side +39.7 mm, tyre diameter +10.8 % : fit it with the original tyre size of Rover 100-Serie (155/65R13), not that of Triumph TR8.
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 Rover 100-Serie (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 Rover 100-Serie on Triumph TR8?