Impossible to answer without context.
If you're a family with a big mortgage, childcare costs and an insecure income, tens of thousands could run out in months if you lost your income.
If you have a pension that covers your outgoings and own an energy efficient paid for property in good repair, you could feel happy with minimal savings, well under £5k because its not foreseeable that you'll be short of money.
If you're in secure rented housing and are used to not having much spare money, a few hundred spare, enough to replace the washing machine and buy a few treats could feel like a huge amount.