concur fully with ATNotts
dutch bulb fields tours by air for either a day or short trips were huge business back then in the quiet shoulder period before the summer season kicked off
look at some old photos of RTM and you will see maybe a 10 or more UK charter a/c on the deck
clarksons were one of the biggies but many companies enjoyed the work (same with JER and GCI holidays by air - nowadays the popularity has long waned)
nowadays most bigger and local coach holiday companies (we have 4 down here in west dorset) all offer trips to the bulb fields by coach/ferry from your local town and are usually a sell out