Most employees (at least in the US) aren't given a contract, they're given an offer of employment. This provides no guarantees as to what work you'll do, or the conditions you'll do it in, and both can change at any time.
An offer of employment is a contract, if there is an exchange of benefits involved in the agreement (you work for us X days a week, we pay you Y).
Even if it's only verbal, it's a contract; contract law applies, and if you can prove the conversation happened, you can enforce the contract in law.
This is the same in the USA and in the UK. But of course, it's much better to get a written contract before starting work (or moving home, if that's what it comes down to).
And (of course) it's much harder for an employee to enforce a contract against an employer than v.v. Contract litigation can be very expensive.
It is very common for employment offer letters in the US to clearly specify that employment is offered at will. This status has slightly different exceptions by jurisdiction, but in general, it means the agreement can be terminated at any time by either party.
Most people summarize this as "you can be fired for no reason", because that's the most commonly discussed scenario. But, your employer doesn't have to terminate your employment to terminate your employment agreement.
> At-will also means that an employer can change the terms of the employment relationship with no notice and no consequences. For example, an employer can alter wages, terminate benefits, or reduce paid time off.
Now, they can't do this retroactively, but they can do it with zero notice.
In the UK, your contract is formed by: the thing you signed, any statutory law stuff, and any custom and practice stuff in your workplace. Generally speaking however, it's the same as what other people in this subthread have pointed out: you probably can't do a lot if the employer changes your contract, either officially or unofficially. Continuing to go to work implies acceptance and well. You could attempt to take the employer to an employment tribunal,but they're expensive (even more expensive thanks to the recent Conservative governments)
Source: used to be a trade union official. If there was a union for tech jobs, they might be able to pay for tribunal costs, but when I did it we only took them on if there looked to be a greater than fifty percent chance of winning.
I am a member of the Digital Division Committee of Prospect/Bectu Committee. We do take cases for existing members.
Unison has few places it represents at (probably more for historical reasons).
How ever apart from the costs we would only take a case to tribunal if it was a good chance of winning - as the pressure on the member going through a case is considerable.
Breach of contract is not illegal. It's a tort, and you might be able to seek recompense through the courts, but I don't know how they would determine damages.
