The largest victory in England vs Pakistan one day international (ODI) is 198 runs with which England beat Pakistan at Trent Bridge in Texaco trophy match back in August 2010..
Star-studded Pakistan bowling comprising Wasim Akram, Waqar Yonus, Aaqib Javed and Mushtaq Ahmed were thrashed allround the park that day by Robin Smith (77 off 72), Neil Fairbrother (62 off 63) and Graeme Hick (63 off 42) after captain Graham Gooch and Alec Stewart put on 84 for the opening wicket after green team had elected to field first. England posted mountainous 363 for 7 wickets in that 55 over per side one day cricket match and visitors slipped to 165 allout inside 46.1 overs. Fast bowler Philp DeFreitas (3 for 33) and spinner Ray Illingworth (3/34) did most of the damage and gave Pakistan a dark spot they still haven't been able to wash off.
Pakistan's biggest one day win over England is by 165 runs, achieved at National stadium in Karachi on 15 December 2005. this time England captain Marcus Trecothick had elected to field first and watched his mates chase leather for 353 from from only 50 overs (Kamran Akmal 109, Mohammad Yousuf 68, Shahid Afridi 31, Inzamam-ul-Haq 45, Abdul Razzaq 51 off 22 balls). England were allout for 188 in 42 overs.
Note that England & Pakistan have never beaten each other by 10 wicket margin ever. Most dominant result has been 8 wkts win margin which Pakistan have done twice (at Edgbason in 1974 & Lahore in 2000) and England once (at Lord's in 1983).
The smallest, or I should say the most interesting England v Pakistan one day international in terms of victory margin is 2 run difference at Lord's on 12 June 2001. Mohammad Yousuf's patient 81 off 119 balls and then quickfire 27 off 21 balls by Azhar Mahmood pushed Pakistan to a respectable 242 but Marcus Trecothick looked determined to snatch the match out of visitors hands. 137 from 142 balls with 11 fours and 3 sixes, Trecothick was 9th batsman out in 50th over bowled by Saqlain Mustaq and his team fell to a marginal 2 run defeat.
Pakistan have also beaten England by 3 runs, at same venue back in year 1992 while England's razor sharpe win over Pakistan in ODI is 6 runs, registered at Rawalpindi on 2005 tour.
In terms of wickets, England's last pair Neil Foster and Greg Thomas gave them crucial 8 runs to close out the match with 3 balls remaining. Philip DeFretias played a magical innings of 33 off just 22 balls that day to give home team a sniff and they got home after being 8 down for 167 chasing 214 from 55 overs.