Nested fuctions

I was learning to do some nested functions and was applying this to a scenario, whereby I have intercompany balances which could be either Debit or Credit balances analysed by either a "UK" or an overseas company (see attached spreadsheet).The overseas I have called "other". I wanted to get a function that would be able to get me the UK Debtor (postive) balances and UK Creditor balance (Negative) balances. Similarly i wanted the formula to give me the Other Debtor and Other Creditor balances. I wanted the formula/funtion in the area highlighted in the colour "Green".

I have tried using the "SUMIF" Function usinf the ">0" and the <0 as a criteria but can only get an answer for the overall debtor or creditor but not segregate between UK and Other. I thing I nesting another function in the "SUMIF" function could get me the result but I am struggling a bit (maybe the combination of the vlookup and sumif!!

Can you please help?