Pension Lifetime Allowance

I keep hearing about the UK Pension Lifetime Allowance and possible changes coming in the budget.  I haven't been able to find out too much about whether this applies to US pensions, social security, 401ks, and IRAs.  The standard Lifetime Allowance is currently £1,073,100 (2020-2021).  Can anyone enlighten me?

Thanks.

I am pretty sure that it does not apply to US pensions.

The aim of the law is to limit the amount of HMRC tax deferred money you can have before paying tax, and applies to UK defined pension plans and defined contribution plans where pre-tax money has been used to fund them.  In accumulating US pensions no HMRC tax has been deferred. 

Agreed. 
https://www.legislation.gov.uk/ukpga/2004/12/section/214
FA 2004 s214 says charge to income tax, to be known as the lifetime allowance charge, arises where—
(a)a benefit crystallisation event occurs in relation to an individual who is a member of one or more registered pension schemes,

see underline by me.

Agreed. 
https://www.legislation.gov.uk/ukpga/2004/12/section/214
FA 2004 s214 says charge to income tax, to be known as the lifetime allowance charge, arises where—
(a)a benefit crystallisation event occurs in relation to an individual who is a member of one or more registered pension schemes,

see underline by me.

Excellent, thanks for the informative link.

Thanks.  That makes me feel a lot better.  I didn't fancy trying to figure out what the "value" of all my retirement assets were when I start drawing down my IRA and receiving my pension.