Today's Tech: MPs demand Google's head for tax evasion and NSA chief claims Prism is an anti-terrorism shield

A panel of MPs has called for HM Revenue and Customs to step up its investigation into Google's tax arrangements. The Public Accounts Committee (PAC) says it has learned from former Google employees that UK-based Google workers are involved in advertising sales, which would make Google liable for full taxation by HMRC. Google, meanwhile, claims its advertising operations take place in low-tax Ireland and not in the UK. Google does employ sales forces in the UK, but VP Matt Brittin maintains that none of them has the authority to execute transactions. The Internet giant made $18 billion (£11.5 billion) in revenue from 2006 to 2011 but only paid $16 million (£10.2 million) in corporation tax, which is based on company profits. The PAC believes that HMRC's failure to act has caused the organisation to lose credibility, and that loopholes in the tax code need to be ironed out.

Around 100,000 workers based in London's swish Canary Wharf quarters will get free public Wi-Fi, in a bid by Telefonica's O2 to raise its profile amongst this very influential audience. As an additional bonus, you won't need to be an O2 customer in order to benefit from the facility. The infrastructure for the Wi-Fi service is being installed on behalf of the Canary Wharf Group which manages the location and is expected to go live at some point this year. Wi-Fi users will only need to register once and will be automatically signed in on future visits. The service will presumably be financed by advertising, judging from O2's statement that visitors to Canary Wharf are "incredibly valuable to retailers and advertisers," with nearly half of them dealing in shares.

NSA chief Keith Alexander has attempted to justify surveillance programme Prism by claiming it enabled the break-up of several terrorist schemes. In a US Senate hearing, Alexander defended the Internet and telephone spying initiatives, following its recent exposure by a former CIA contract worker. President Barack Obama has confirmed that Prism was closely overseen by both Congress and America's legal system. US Secretary of State John Kerry has also piped up, and believes that - despite the blatant invasions of privacy - members of the public will appreciate the spying network once they "understand it." Alexander added that intelligence officials were "trying to be transparent" about the programmes, however, the NSA boss said that details would be withheld "because if we tell the terrorists every way that we're going to track them, they will get through and Americans will die."

Finally, Apple is reportedly considering making new iPhone devices with significantly larger screens, which would put the company in stronger competition with Samsung's growing "phablet" range. Sources, including Asian suppliers, suggest Apple wants to launch two larger form factor iPhones in 2014, a 4.7in model and a 5.7in model, effectively mirroring the sizes of Samsung's Galaxy S and Note smartphones. Apple has allegedly approached suppliers with plans for the larger devices, suggesting this is more than just an idea, but there is nothing concrete yet. Apple has already adjusted the size of its smartphone screen in the iPhone 5 released last year, which touts a 4in display, compared to the traditional 3.5in display that has been employed in all previous iPhone models; a shift away from Steve Jobs' design principles. Apple would have some tough competition on its hands, though, with Samsung's 5in Galaxy S4 and rumoured 6in Galaxy Note 3 set to dominate the industry.