The /ɔ/ vowel is spelled <or>, <oor>, <oar>, <au> and <aw>. The /ʊə/ diphthong is spelled <oor>, <our>, <ure>, <ewe> in crewel and <ue> in cruel. The contrast saw/sewer would not be minimal if one treats sewer as a two-syllable word. There is a difference of stress in the pair inshore/insure. For many speakers the word lure contains a palatal glide which would make in non-minimal in its various contrasts.
Although this is a contrast between a long vowel and a diphthong, the starting positions are fairly close and confusions can easily occur. Some RP speakers, especially speakers of an old-fashioned variety, conflate these phonemes, using /ɔ/ throughout.
Interesting pairs include:
The density figure is 3.23%. The set makes 33 semantic contrasts giving a high loading of 82.3%.
ashore assure boar boor boars boors bore boor bores boors crawl crewel crawls crewels crawl cruel crawler crueller Crawley cruelly Dawley dourly daw dour door dour gaud gourd gored gourd hoary houri inshore insure laud lured law lure laws lures lor lure lord lured Maud moored maw moor maws moors more moor paw poor pore poor pour poor saw sewer shore sure sore sewer spore spoor spores spoors tor tour tors tours tor Tours tore tour tore Tours yore you're
John Higgins, Shaftesbury, July 2014