One other option with a "late" train is Filton Abbeywood.
For me all the train options fail my penultimate train on the schedule test as IMHO planning to catch the last train anywhere is not worth the risk nowadays.
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Full details here https://traffic.wales/current-projec...-waterproofing
This coming weekend the closure is East bound. I would leave the M4 at junction 28, Tredgar House and follow the docks link road south of Newport and rejoin the M4 at The Coldra