I live in Finland.
The work I do for the UK organisation is done partly in UK, partly in Finland and partly in other countries.
The work I do for the international organisation is done partly in Finland and partly in other countries.
I'm back.Take a look at the UK/Finland double tax treaty here. Article 16 deals with employment income.To the extent that the work for the UK organisation is done in the UK, then the salary from that job will be taxable in the UK. The balance will be taxable in Finland. You may need to split the income into two periods, one of days worked in the UK and one of days worked outside the UK.The income for work done for the international organisation will be taxable in Finland unless that organisation has agreements with the other countries where you do the work or tax treaties Finland has with those countries dictates such that some of the income will be taxable in those countries. If that is the case, any non-Finnish tax paid will be deductible from your Finish tax liability. Article 16 paragraph 2 will tell you whether any of the pay will be taxable in another country including the UK. This paragraph is present in many tax treaties.Some international organisations such as the United Nations have tax exemptions for their employees.I hope this helps but let me know if you have any further questions.