This is what HiFX say on their website:
As one of the largest and most established currency specialists in the UK, HiFX works hard to keep your money safe.
Regulatory Information - HiFX PLC is authorised and regulated by the Financial Services Authority under the Payment Services Regulations 2009, registration number 462444, for the provision of payment services. HiFX PLC also a registered MSB with HM Revenue & Customs – registration number 12131222
Online Security - HiFX Online is VeriSign secured. The VeriSign seal is the most recognised trust mark on the internet and helps companies and consumers all over the world to engage in trusted communications and commerce billions of times every day. 97 of the world's 100 largest SSL-using banks and over 93% of Fortune 500 companies use SSL Certificates sold by VeriSign. In addition, VeriSign secures more than one million Web servers worldwide, more than any other Certificate Authority.
Payments & Settlements - HiFX is one of the only currency specialists in the world with direct access to SWIFT. SWIFT is the world's largest payments and settlements network for domestic and international trades. Direct access ensures HiFX clients, benefit from faster payments and enhanced security.
Security of Funds - When buying currency with us your funds are held either in pooled client trust bank accounts or are held at one of our counterparty brokers as cash in transit or collateral to meet our obligations relating to clients’ trades.
Funds can be used to fulfil the contractual obligations of our clients but will never be anywhere other than:
- In the segregated client accounts
- With our banking counterparties (Barclays; Deutsche Bank; Citigroup or Bank of Ireland Wholesale).
- In transit i.e being sent.
We have held our segregated client trust accounts with Barclays for the last twelve years and I can provide you with a letter from Barclays which confirms this relationship.
http://www.hifx.co.uk/personal/guide_to_our_service/your_security.aspx