Bit of news on the running Bantam: Turns out that the reason it stopped running is because brains of Britain here got the choke the wrong way, i.e thought it was off and it was on. Someone kindly pointed out which way it should be, and it was great afterwards. Too the chance to hoy the old stinking fuel out and pre-mixed some E5 Shell with synthetic 2T oil, also Shell. The previous owner suggested not using synthetic, but some internet research from fellow owners said it wouldn't do any harm, and it certainly hasn't effected the Lambretta. Sods law dictates piddling down for days (fair weather biker) and having to use a van for work as I had three other bikes to move about, so not been out on the BSA since.
In other news, the RD50 is back from the garage. The headstocks bearings were alarmingly shot, so newer fancier ones have been fitted and a running issue (won't rev past about 5,000) was supposedly sorted. It's fine in first, but bogs down something chronic under load (17.5 stone fat bloke) so going back to garage. They seem a decent outfit so it's no biggy as it stands.