The comparison goes roughly like this, obviously the UK figures are less detailed so I've grouped some of the US expenditure where I think appropriate, correct me if you see any errors.
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UK: Pensions £1,459.32 ($2,310.61) + Welfare £705.73 ($1,117.42)
Total= $3,4328.03
US: Social Security: $1908.03 + Housing $133.78
Total = $2,041.81
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UK: Healthcare £1,453.33 ($2,301.13)
Total = $2,301.13
US: Medicare $1274.89 + Medicaid $816.32 + Healthcare $221.62
Total = $2,312.83
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UK: Education £364.83 ($577.65)
Total = $577.65
US: Education $131.50
Total = $131.50
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UK: Defence £532.29 ($842.80)
Total = $1,117.42
US: Defense $1869.09 + Veterans Affairs $147.84
Total = $2,016.93
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UK: Protection £197.37 ($312.50) - nb. (Includes Police Services, Fire-Protection Services, Law Courts, Prisons,Public Order and Safety)
Total = $312.50
US: Homeland Security $123.76 + Department of Justice $67.31 + Potential Disaster Allotment $30.73
Total = $221.80
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UK: Transport £161.48 ($255.67)
Total = $255.67
US: Transportation $204.17 + Public Engineering $14.33
Total = $218.50
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UK: General Government £155.50 ($246.21)
Total = $246.21
US: Department of State $145.26 + Department of Energy $74.05 + Department of Agriculture $73.21 + Treasury $37.45
Total = $329.97
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UK: Interest Paid £334.92 ($530.29)
Total = $530.29
US: Interest on National Debt
Total = $461.64
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UK: Other Government Spending £616.02 ($975.37)
Total = $975.37
US: NASA $52.67 + Commerce $38.84 + Labor $37.45 + Natural Parks $33.79 + Environmental Protection Agency $29.57 + National Science Foundation $19.69 + National Infrastructure Bank $14.06 + Community Service $3.08 + Small Business $1.93 + Bureaucracy $1.54 + Everything Else $55.75
Total = $125.62
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Finally: Miscellaneous mandatory programs $1606.83
Wasn't sure what this included, maybe US readers can shed some light upon how this might relate to the above sections. Obviously the main mismatch is in the other government spending so maybe most of that belongs in there.
Anyway not exactly like for like but may be an interesting excercise.