There is no single official cost of immigration.
'What does immigration really cost?' There is no single official number, anyone who gives you one is guessing. Here's the honest ledger, both sides. (The £4.9bn you hear quoted is the asylum system alone.)
8 figures, each with its official source.
To produce one you must net migrants' use of every public service against the income tax, NI, VAT, visa fees and NHS surcharge they pay, and the answer flips sign by route. No official body publishes a single total.
Housing, cash support and processing for ~100,000 people awaiting a decision, under 1% of the UK's ~10.6m foreign-born residents. It is the visible, badly-run slice, not the whole cost.
≈£3.0bn visa/immigration fees + ~£2.4bn NHS surcharge + ~£0.6bn Immigration Skills Charge, before income tax, NI and VAT, which aren't recorded by nationality and so can only be modelled.
Higher net migration lowers government borrowing because migrants are overwhelmingly working-age taxpayers. A scenario, not a promise; lower migration worsens the finances symmetrically.
Skilled worker +£689k · family −£109k · low-wage & humanitarian negative Lifetime net present values by route. The average across all routes sits far below the skilled-worker figure, which is the whole point: it is not one number.
About 1 in 6. Includes millions of naturalised British citizens and long-settled residents, presence, not an annual cost.
Why cities feel saturated while the national picture (16%) and the cost question are different things. Migration concentrates in cities.
A large share of NHS, care, hospitality & construction workers were born abroad Migrants fund and run public services as well as use them, the point a costs-only ledger erases. Exact shares vary by sector; see the Migration Observatory overview.