Usefull links:

Below you can find some useful information about Self-Assessment, Tax Return, National Insurance Contribution, and many more.
https://www.gov.uk/government/organisations/hm-revenue-custom

Below you can some foreign exchange monthly rates from the current and previous years.
https://www.gov.uk/government/organisations/hm-revenue-custom

Below you can find some Income Tax rates and allowances for current and past years.
https://www.gov.uk/government/publications/rates-and-allowances-income-tax/income-tax-rates-and-allowances-current-and-past

Below you can find some rates and allowances for National Insurance Contributions.
https://www.gov.uk/government/publications/rates-and-allowances-national-insurance-contributions/rates-and-allowances-national-insurance-contributions

On this page you can pay your Self-Assessment tax bill. All you need is your UTR number, amount to pay and your card payment details.
https://www.tax.service.gov.uk/pay-online/self-assessment

On this page you can pay your employer’s PAYE and National Insurance. To do that, you will need Account Office reference (you can find it on the letter from HMRC, when you first registered for PAYE), amount to pay and card payment details.
https://www.tax.service.gov.uk/pay-online/epaye

You can pay your Corporation Tax here. You will need your Payslip reference (your Payslip reference is shown on your payslip you receive from HMRC or your accountant. It’s made up of 17 characters, for example 1234005678A00101A), amount to pay and card payment details.
https://www.tax.service.gov.uk/pay-online/corporation-tax

On this page you can pay your VAT. You need your VAT registration number (VRN), VAT accounting period ending eg 04 2018, amount to pay and card payment details.
https://www.tax.service.gov.uk/pay-online/vat