TheUnitedKingdomisaconstitutionalmonarchy:QueenElizabethIIisheadofstateoftheUKaswellasoffifteenotherCommonwealthcountries,puttingtheUKinapersonalunionwiththoseotherstates.TheCrownhassovereigntyovertheCrownDependenciesoftheIsleofManandtheBailiwicksofJerseyandGuernsey,whicharenotpartoftheUnitedKingdomthoughtheUKgovernmentmanagestheirforeignaffairsanddefenceandtheUKParliamenthastheauthoritytolegislateontheirbehalf.

　　TheUnitedKingdomhasanuncodifiedconstitution,[37]asdoonlytwoothercountriesintheworld.TheConstitutionoftheUnitedKingdomthusconsistsmostlyofacollectionofdisparatewrittensources,includingstatutes,judge-madecaselaw,andinternationaltreaties.Asthereisnotechnicaldifferencebetweenordinarystatutesand"constitutionallaw,"theUKParliamentcanperform"constitutionalreform"simplybypassingActsofParliamentandthushasthepowertochangeorabolishalmostanywrittenorunwrittenelementoftheconstitution.However,noParliamentcanpasslawsthatfutureParliamentscannotchange.[38]

　　TheUKhasaparliamentarygovernmentbasedontheWestminstersystemthathasbeenemulatedaroundtheworld—alegacyoftheBritishEmpire.TheParliamentoftheUnitedKingdomthatmeetsinthePalaceofWestminsterhastwohouses:anelectedHouseofCommonsandanappointedHouseofLords,andanyBillpassedrequiresRoyalAssenttobecomelaw.ItistheultimatelegislativeauthorityintheUnitedKingdomsincethedevolvedparliamentinScotlandanddevolvedassembliesinNorthernIreland,andWalesarenotsovereignbodiesandcouldbeabolishedbytheUKparliamentdespitebeingestablishedfollowingpublicapprovalasexpressedinreferenda.

　　TheHousesofParliamentThepositionofPrimeMinister,theUK'sheadofgovernment,belongstotheMemberofParliamentwhocanobtaintheconfidenceofamajorityintheHouseofCommons,usuallythecurrentleaderofthelargestpoliticalpartyinthatchamber.ThePrimeMinisterandCabinetareformallyappointedbytheMonarchtoformHerMajesty'sGovernment,thoughthePrimeMinisterchoosestheCabinet,andbyconventionHMTheQueenrespectsthePrimeMinister'schoices.[39]

　　TheCabinetistraditionallydrawnfrommembersofthePrimeMinister'spartyinbothlegislativehouses,andmostlyfromtheHouseofCommons,towhichtheyareresponsible.ExecutivepowerisexercisedbythePrimeMinisterandCabinet,allofwhomareswornintoHerMajesty'sMostHonourablePrivyCouncil,andbecomeMinistersoftheCrown.TheRtHonGordonBrownMP,leaderoftheLabourParty,hasbeenPrimeMinister,FirstLordoftheTreasuryandMinisterfortheCivilServicesince27June2007.[39]

　　ForelectionstotheHouseofCommons,theUKiscurrentlydividedinto646constituencies,with529inEngland,18inNorthernIreland,59inScotlandand40inWales,[40]thoughthisnumberwillriseto650atthenextGeneralElection.EachconstituencyelectsoneMemberofParliamentbysimpleplurality.GeneralElectionsarecalledbytheMonarchwhenthePrimeMinistersoadvises.ThoughthereisnominimumtermforaParliament,theParliamentAct(1911)requiresthatanewelectionmustbecalledwithinfiveyearsofthepreviousgeneralelection.

　　TheUK'sthreemajorpoliticalpartiesaretheLabourParty,theConservativeParty,andtheLiberalDemocrats,whowonbetweenthem61