Which is the best broker in the U.K.?

I am not in the UK. Will you be able to provide more information as to what you are looking for in a broker so others can help you? Are you looking for a broker based in the UK? What will you be trading? What trading platform are you looking to use?

The first thing to consider will be the tax implications. If you are a casual swing trader, it would make sense to open a Spread-Bet account as any gains are tax free. HMRC thinks you will lose rather than win - they let you have the profits, but you can't claim the losses.

If you are more serious and intend to pay tax on gains, you will likely want to offset losses and claim expenses. If you're a swing trader, then a CFD account will be convenient. You'll pay around a tick on entry/exit, but you can fund the account instantly with a debit card, and withdraw for free.

For both Spread-Bet and CFD accounts, I have found IG.com to be quite good.

If you're a scalper or trade order flow, then you will almost certainly benefit from opening a proper futures account with a dedicated data feed and platform. I would recommend Interactive Brokers UK. They have very cheap commissions. However, they only offer standard margin, so they won't be suitable if you are a daytrader requiring high leverage. They also have a maintenance window each night during the Asian session, so you can't use them if that is what you want to trade.

Disadvantages of using a US broker:

• US brokers do not accept transfers from the challenger banks (Revolut, Wise, etc) due to KYC rules, so you'll need a US Dollar account with HSBC or some other regular bank. Wire transfer fees can be expensive.
• Lack of FCA protection in case the broker goes bust.
• Need to consider GBPUSD exchange rate.
• Broker support is likely to be closed during the Euro session.

Advantages of using a US Broker:

• Margin
• Service (via your Introducing Broker)

Some smaller brokers like AMP Futures allow you to be a direct customer. This will work out cheapest on commissions, but be prepared for marginal service. Most of the larger brokers (e.g. ADMIS) require you to go via an introducing broker. You should expect very good service from your Introducing Broker.

Personally I use Optimus Futures and am happy with them.