The spelling of /b/ is always either <b> or <bb>. The /v/ sound is here always spelled <v>.
The contrast is between two voiced consonants, one plosive and one fricative, fairly close in the mouth. It is notoriously a problem for Spanish speakers. On a trip to Spain I remember hearing a Spanish guide leading a party of British tourists asking them to rendezvous at what they all thought was "St Martin's Village" when he meant to say "St Martin's Bridge". The /b/ versus /v/ contrast is not made in Spanish, and his strong articulation of the /r/ made it easily confused with an /l/. Other speakers may have occasional difficulties, especially when the contrast occurs in syllable-final position.
One pair with a slight potential for embarrassment is lab/lav.
Interesting pairs include
bicker vicar
bigger vigour
biking Viking
burble verbal
knobble novel
The mean density value is 1.8%. The list makes 77 semantic distinctions, a loading of 53%.
Aveley ably B V B's V's baas vase back vac backs vacs bail veil bailed veiled bailing veiling bails veils bail vale bails vales balance valance balances valances bale veil bales veils baling veiling baled veiled bale vale bales va;les ballet valet ballets valets bally valley bane vain bane vein banish vanish banished vanished banishes vanishes banishing vanishing bat vat bats vats BC VC beano vino beard veered becks vex beer veer beers veers Belem vellum belt veld bend vend bended vended bending vending bends vends bent vent bents vents best vest bested vested besting vesting bests vests bet vet betted vetted betting vetting bib Viv bicker vicar bickers vicars bide vied bier veer biers veers bigger vigour biking Viking bile vile binary vinery bine vine bines vines biz viz boat vote boated voted boating voting boats votes boater voter boaters voters boil voile bole vole boles voles bolt volt bolts volts bow vow bows vows bowed vowed bowing vowing bowel vowel bowels vowels box vox Bulgarian vulgarian Bulgarians vulgarians buoyed void burble verbal burst versed bury very buy vie buying vying buys vies by vie bye vie byes vies cupboard covered curb curve curbed curved curbing curving curbs curves dub dove dubs doves dribble drivel dribbled drivelled dribbles drivels dribbler driveller dribblers drivellers fibre fiver fibres fivers gabble gavel gabbles gavels gibe jive gibed jived gibes jives gibing jiving grebe grieve grebes grieves hobble hovel hobbles hovels Job Jove knobble novel knobbles novels Lab lav labs lavs lobes loaves lubber lover lubbers lovers marble marvel marbled marvelled marbles marvels ob of rebel revel rebels revels robe rove robed roved robes roves robing roving sabre savour sabred savoured sabres savours sabring savouring TB TV verb verve Woburn woven
John Higgins, Shaftesbury, January 2010.