What tends to put downwards pressure on wages is not availability of labour, but degree of protections of workers.
If you can sack your current workers easily then you can avail yourself of cheap new ones - and if those don't work out you can repeat the process.
If you need to manage your existing workers out according to due legal process then they have to have done something wrong - and the process takes time. Also you can't make them redundant and then hire someone else for the same role as that's against the rules.
So there might be a huge pool of cheaper workers available, but you can't "swap" your expensive ones for them.
Zero hours contracts changes this - you can be given hours from zero to whatever, no need to follow legal process to get rid of you - you simply don't get any hours.
What tends to put downwards pressure on wages is not availability of labour, but degree of protections of workers.
If you can sack your current workers easily then you can avail yourself of cheap new ones - and if those don't work out you can repeat the process.
If you need to manage your existing workers out according to due legal process then they have to have done something wrong - and the process takes time. Also you can't make them redundant and then hire someone else for the same role as that's against the rules.
So there might be a huge pool of cheaper workers available, but you can't "swap" your expensive ones for them.
Zero hours contracts changes this - you can be given hours from zero to whatever, no need to follow legal process to get rid of you - you simply don't get any hours.