Birmingham law firm Blakemores says it is outrageous that accident victims are being left to suffer.
It has made a renewed call for greater co-operation between claimants' and defendants' insurers to ensure that victims are offered rehabilitative treatment as soon as possible.
The plea comes in the light of recent NHS surveys which reveal that patients have to wait an average of seven weeks just for diagnostic tests.
The so-called rehabilitation code that forms part of the personal injury pre-action protocol promotes early rehabilitation and intervention so as to enable the injured party to make the quickest and best recovery possible.
Under the code, both parties in the claims process are encouraged to communicate early regardless of the severity of the injury and consider whether rehabilitative treatment may be appropriate.
Independent medical assessments are supposed to identify rehabilitative needs so that treatment, for example physiotherapy, can be arranged in the early stages on a private basis rather than people face lengthy waiting lists having to rely on the NHS.
Where liability has been admitted, the costs of the treatment is met by the defendant or their insurers and can be released as an interim payment on account of damages rather than wait until the conclusion of the claims process, which is often too late.
Kellie Maguire, a Blakemores solicitor specialising in claimant personal injury work, said: "All too often people fail to appreciate the significant impact that an injury can have upon the life of the innocent injured party.
"While the rehabilitative code raises awareness for the need for communication between claimants and defendants to identify appropriate rehabilitative treatment at an early stage, the code is unfortunately not compulsory.
"There are many occasions where requests are made for interim payments to be released so that early treatment can be arranged but the defendant insurers are often reluctant to do so without medical evidence having been finalised, which can take months and this is clearly too late."