You attach nothing to a UK return.
With a US return you need to attach a W-2, or 1099 or 1042-S but only if there is US withholding tax to claim. You do not attach P60s, P45s or payslips or foreign tax returns.
You do have to file - at least - 1040, Schedule B, 2555 and/or 1116, 8965, possibly 8938 and FinCEN 114. Enjoy.