Check online as last time I checked a month ago, there was no post to the UK via the post office. If there is, there is no option for surface mail.
A few years ago, I sent my bike back while on a trip to HK as surface mail.
I’m flying Singapore airlines, allowed 25kg bike 8.5 so boxed up maybe 10kg. seems I’m gonna have to keep luggage weight down and take bike on plane hoping be ok boxed up in proper bike box and small case allowed?
Won’t be using DHL