Before you start

A National Insurance number
PAYE registration through your employer, or Self Assessment registration if you freelance
A Government Gateway account
Records of foreign income and overseas accounts

Step-by-step

1
Check the tax code on your first payslip
PAYE deducts at source, so a wrong code means wrong deductions for months before anyone notices. Your code should not begin with an S — that is the Scottish prefix — or a C, which is the Welsh one. Both get applied in error by payroll teams run from elsewhere.
Via employerWho: YouFirst payslip
2
Learn the three English bands
A personal allowance, then Basic, Higher from £50,270 and Additional from £125,140. The thresholds have been frozen for several years, which quietly pulls more people into higher bands each year as wages rise.
OnlineWho: You
3
Understand the 60% trap above £100,000
The personal allowance is withdrawn by £1 for every £2 earned above £100,000, giving an effective marginal rate of about 60% between £100,000 and £125,140. Pension salary sacrifice is the standard response. It is the most consequential quirk in the English system and it is signposted nowhere.
OnlineWho: You
4
If you freelance, register for Self Assessment early and understand payments on account
Register with HMRC as self-employed within the required window after starting. The trap is payments on account: in your second year you pay the previous year's bill plus two instalments toward the next, which for a first profitable year can mean settling roughly 150% of a year's tax in one January. Set money aside from every invoice from day one — a separate account, not a mental note.
OnlineWho: You
5
Do not expect the freeport to change your personal tax
The Solent Freeport gives authorised businesses inside its customs site at the port simplified customs procedures and tariff suspension, and businesses locating on the tax site at Dunsbury Park business rates relief and other incentives. It is a corporate regime tied to specific plots of land. Living in Portsmouth, or working for a company inside it, does not change your income tax or National Insurance at all.
OnlineWho: You
6
Settle your residence position in year one
The Statutory Residence Test determines UK tax residence from days present and connecting factors. The UK abolished the old non-domiciled regime and replaced it with a residence-based system, and the transitional rules are genuinely complex. Take advice in the first year if you have foreign income or assets.
In personWho: You

Documents you’ll need

National Insurance number
P60 — the annual summary from your employer
P45, if you change employer during the year
Invoices, expenses and bank records, if you freelance
Government Gateway credentials, for Self Assessment

Things most newcomers don’t know

A freeport is a business regime attached to a plot of land, not a low-tax city.

Portsmouth is inside the Solent Freeport — the customs site is at the port itself, the tax site is at Dunsbury Park — and the phrase does a lot of work in property marketing. It confers customs simplifications and business rates relief on qualifying businesses at those specific sites. It changes nothing about the income tax, National Insurance or Council Tax of a person who moves here.

Source: Portsmouth International Port — Solent Freeport

The 60% band between £100,000 and £125,140 is the biggest hidden rate in the system.

The personal allowance is withdrawn at £1 for every £2 above £100,000, so each extra pound in that range is taxed at the 40% headline rate plus the lost allowance — around 60% in effect. Model it before accepting an offer in that range and look at salary sacrifice.

Source: GOV.UK — income tax rates and personal allowances

Payments on account are the reason a first freelance January hurts.

In the January after your first profitable self-employed year you settle that year's tax and simultaneously pay the first instalment toward the next — commonly about 150% of a normal year's bill at once, with the second instalment following in July. It is entirely predictable if you set money aside from each invoice, and a genuine shock if you do not.

Source: GOV.UK — understand your Self Assessment tax bill

The tax year runs 6 April to 5 April, which catches everyone once.

Almost no other country uses these dates. It decides which year your arrival income falls into, when your P60 arrives, and when Self Assessment is due. Newcomers routinely reckon against a calendar year and get their first filing wrong.

Source: HMRC

Common mistakes to avoid

Believing property marketing that implies freeport status is a personal tax advantage.
Not checking the PAYE code on the first payslip, especially for a stray Scottish S or Welsh C prefix.
Accepting a salary between £100,000 and £125,140 without modelling the 60% effective band.
Freelancing for a year without setting aside tax, then meeting payments on account in January.
Counting the tax year as January to December rather than 6 April to 5 April.

Some of this may be out of date. Spotted something inaccurate? Help us keep it right for the next newcomer.