The spelling of /p/ is always <p> or <pp>. The /ʧ/ sound is normally <ch> or <tch>, though we also see <tu> in suture, torture and vesture, and it occurs in the letter name H.
The contrast is between a plosive and an affricate, both voiceless but well separated in the mouth. There is little risk of confusion.
Interesting pairs include:
dapper dacha
Epping etching
panel channel
perish cherish
pillion Chilean
purpose purchase
torpor torture
vespers vestures
The mean density value is 3.4%. The list makes 152 semantic distinctions, a loading of 51%.
ape H beep beach beep beech bleep bleach bleeped bleached bleeping bleaching burp birch burped birched burping birching cap catch capping catching chirp church cope coach coped coached coping coaching creeper creature creepers creatures crop crotch dapper dacha dip ditch dipped ditched dipping ditching Epping etching gulp gulch hap hatch happed hatched happing hatching hip hitch hippies hitches hoop hooch kip kitsch lap latch lapped latched lapping latching leap leach leaped leached leaping leaching leap leech leper lecher lepers lechers map match mapped matched mapping matching nip niche P’s cheese pa char pace chase paced chased paces chases pacing chasing paced chaste pad Chad pah char pain chain pained chained paining chaining pains chains pair chair paired chaired pairing chairing pairs chairs palace chalice palaces chalices palm charm palmed charmed palming charming palms charms palmer charmer palmers charmers pane chain panes chains panel channel panelled channelled panelling channelling panels channels pap chap pap patch par char pars chars pare chair pared chaired pares chairs paring chairing parity charity parley Charlie Parma charmer parr char parrs chars parse chars part chart parted charted parting charting parts charts paste chased paste chaste pat chat pats chats patted chatted patting chatting patter chatter pattered chattered pattering chattering patters chatters patty chatty pause chaws pause chores paw chaw pawed chawed pawing chawing paws chaws paw chore paws chores pawky chalky peak cheek peaked cheeked peaking cheeking peaks cheeks peaky cheeky peakier cheekier peakiest cheekiest pear chair pears chairs pearl churl pearls churls peas cheese pease cheese peat cheat peck cheque pecks cheques peck Czech pecks Czechs peck check pecked checked pecking checking pecks checks pecker checker peckers checkers pecker chequer peckers chequers peek cheek peeked cheeked peeking cheeking peeks cheeks peep peach peeped peached peeping peaching peeper cheaper peer cheer peered cheered peering cheering peers cheers peerless cheerless pees cheese peke cheek pekes cheeks Peking cheeking perch church perches churches peri cheery perish cherish perished cherished perishes cherishes perishing cherishing perry cherry pest chest pests chests pester Chester Pete cheat peter cheetah peters cheetahs pick chick picks chicks pickle chicle pied chide pier cheer piers cheers piled child pill chill pills chills pillion Chilean pillions Chileans pimp chimp pimps chimps pin chin pins chins pine chine pines chines pink chink pinked chinked pinking chinking pinks chinks pip pitch pipped pitched pipping pitching pique cheek piqued cheeked piques cheeks piquing cheeking pit chit pits chits pock choc pocks chocs pock chock pocked chocked pocks chocks poke choke poked choked pokes chokes poking choking poker choker pokers chokers poky chokey pooh chew pop chop popped chopped popping chopping pops chops Pope poach poppas choppers poppy choppy pore chaw pored chawed pores chaws pore chore pores chores pork chalk portal chortle portals chortles pose chose pour chaw poured chawed pours chaws pour chore pours chores powder chowder powders chowders pox chocks pox chocs puck chuck pucks chucks pucker chukker puckers chukkers pug chug pugs chugs pukka chukker pump chump pumps chumps punk chunk punks chunks purl churl purls churls purpose purchase purposed purchased purposes purchases purposing purchasing pyx chicks rap ratch reap reach reaped reached reaping reaching rep retch rep wretch repp retch repp wretch rip rich Ripley richly rope roach scrap scratch scrapped scratched scrapping scratching scrappy scratchy scrappier scratchier scrappiest scratchiest snap snatch snapped snatched snapping snatching snip snitch snipped snitched snipping snitching sup such super suture supers sutures torpor torture torpors tortures tup touch vespers vestures whip which whip witch whipping witching whoop hooch whop watch whopped watched whopper watcher whoppers watchers whopping watching wrap ratch
John Higgins, Shaftesbury, January 2010.