He says that the competition created by splitting up NHS services to private companies could cause dangerous fragmentation.
The House of Lords will be debating new rules for the Health and Social Care Act for the role that private firms will have today.
The changes are likely to give more power to individuals such as doctors, nurses and clinicians, but campaigners believe it should be MPs who make these decisions, not individuals.
Prof Terence Stephenson has said in a letter to Lord Howe that he believes this move will mean services from the NHS are not joined together.
The complications from this could be a danger to patients, in particular those patients with serious health conditions who require multiple services from the NHS, and he has requested an urgent meeting to discuss this.
While competition between NHS and private providers already exists in areas such as physiotherapy, hearing tests and dermatology, the new rules mean it could be expanded to many other areas of care.
The private sector already provides some care for NHS patients. Under Labour it was used to provide extra capacity for non urgent operations, allowing patients faster access and shorter waiting times.
Prof Stephenson said he was concerned that healthcare services would be disrupted:
Children and adults with complex serious diseases need a joined-up service. We're very keen that that shouldn't be just like buying a mobile phone.
When you are dealing with very complex things, like transferring patients with complex heart surgery from one part of the country to the other, they need post-operative care and rehabilitation. That all has to be joined up.
If you have a private provider just offering to do one bit of that, we're very worried that the service won't be joined up, that medical records won't be open to everyone and there won't be joint accountability.
A Department of Health (DH) spokesperson said they were working to address the concerns:
The regulations will make sure that doctors and nurses can decide when and where to use competition so they can improve services for patients.
However, we do recognise that concerns have been raised about the way in which the regulations could be understood and we want to do everything we can to address these issues and provide clarity for all concerned.