Ian Hi... not a leccy but pretty well versed in such matters.
Firstly do you have a contract in place with a supplier if so who, and at what contracted KwH rate? The contracted rate will be quoted on the contract and also appears on your bills.
If the wiring and elecrical installation is relatively recent the fuse box / consumer unit will have an ICP fitted,. Although its primary purpose is to protect the supply from overloading, the suppliers use the ICP as a current limiter so that if you attempt to use more than your contracted rate the incoming supply is automatically tripped until you shed some of the load after which you can reset the ICP..
So as a first step, locate the ICP and note its value in Amps it will be print engraved on the ICP.
If the supply or ICP is being tripped with a combination of oven and washing machine it is generally an indication that your contracted tarrif is too low.
One minor point is that if you upgrade to a higher tarrif although the charge for electricity consumed remains the same your daily standing charge will increase a little.
For normal domestic use with a large number of electrical appliances like oven, washing machine, heating and aircon I would suggest a tarrif based on 9.2KwH.
If you come back to this forum there are people aboard who can advise further , but we will need to know the current rating of the ICP and your contracted tarrif with your supplier.
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