Apple Pay, the contactless payment solution built into the electronics giant's iPhone 6, is launching in the UK today.

The system means iPhone users can "tap-and-pay" with their phone for the first time.

The launch marks the first time the software will be available outside the US, and will be on offer to anyone with an iPhone 6 or 6 Plus. It will enable users to tap their phone on contactless payment points to complete transactions - just like a contactless credit card.

The system will also work with the Apple Watch.

Apple has not officially confirmed the date of the launch. However, leaked memos from at least one UK supermarket has made reference to July 14 and a tweet from the HSBC UK Twitter account on Sunday confirmed the date in response to a question on the subject, before being swiftly deleted.

Once live, users of Apple Pay will hold their phone close to a contactless reader while keeping a finger on the Touch ID fingerprint scanner in order to authorise a payment.

Those with the latest iPad Air 2 or iPad mini 3 will also be able to use Apple Pay within apps to make purchases online.

A host of major UK brands and banks have signed up to support Apple Pay at launch, including Boots, Waitrose and the Post Office, with the same spending limit of £20 in place for single contactless transactions.

This is expected to increase to £30 in September.

When it is launched, more than 250,000 locations will accept Apple Pay.

Apple also said that privacy and security is a key part of Pay, with the iPhone maker saying that when a credit or debit card is added, the actual card numbers are not stored on the device, or Apple's servers.

Instead, each transaction is completed with a "one-time unique, dynamic security code".

Rival Google is set to launch their own mobile payment solution, Android Pay, later this year, while Barclaycard has already launched the bPay system, where users can choose between either a wristband, key fob or intelligent sticker for their phone that contains contactless technology and can be linked with any bank account and card.

Contactless payment continues to grow rapidly in popularity, with more than £2 billion spent via the system in 2014, according to the UK Cards Association.

Frustrated Apple customers took to Twitter after finding problems with the service within hours of it launching in the UK.

One user, Phil Walsh, posted: "#ApplePay is here in the UK ... Oh Halifax doesn't have it until autumn? Brilliant."

Another, named only as Sam, tweeted: "help! Getting card not added error message with Apple Pay."

Many were annoyed that not all banks support the new feature.

Alex Fehners said: "Apple Pay is available in the UK. Unfortunately none of my card providers support it."

Tim Davies posted: "So Apple Pay is out in the U.K. but none of my HSBC cards work."

One customer, who gave his name as Joseph, tweeted: "not working. The verification page won't even load in the Apple Watch app."

Others apparently had no problem using the payment method.

David Bain tweeted: "First Apple Pay payment done. As someone who's not had a contactless card, I cannot fault it."

Andy Nicolaides posted: "Well setting up Apple Pay on phone and Watch was pretty seamless."

After initially not being a part of the launch day partnership with Apple, Barclays and Barclaycard announced in a statement that the bank would be joining Apple Pay.

A spokesman for the two said: "We are really excited about the launch of Apple Pay and can confirm that we will bring Barclays debit cards and Barclaycard credit cards to Apple Pay in the future."

Though no joining date has yet been specified, the announcement comes after rumoured extensive talks between Barclays and Apple.

Barclaycard also has its own mobile payment rival to Apple Pay in bPay; a range of wristbands, key fobs and stickers that contain contactless payment technology and can be used to complete transactions.