This is a complex question, which I am afraid needs quite a lengthy answer.
At first sight the suggestion that a redundancy scheme which is more generous to everyone than the statutory scheme could be unlawful does look odd, but what you need to consider is that any benefit that an employee receives which is based on length of service, could be considered indirectly discriminatory on the grounds of age. That is because fewer younger people are able to acquire long service, as they may have only entered the employment market a few years previously.
The Equality Act makes it unlawful to discriminate in employment on the grounds of age but includes various caveats and exclusions from that basic rule. One of the exclusions is the provision of length of service benefits as long as they only applied within the first 5 years of service. In other words it is OK to give someone an extra day’s holiday on reaching 5 years’ service, but not to give them an additional day when they reach 10 years’ service. However, you may be able to do this if you can successfully argue that it reasonably appears to you that this benefit fulfils a business need by, for example, encouraging loyalty, motivating staff or rewarding experience.
Another exclusion is in relation to enhanced redundancy payments. When introducing age discrimination legislation, the Government kept the age-related bandings for statutory redundancy pay, arguing that there was justification for doing so. The Act states that employers can make enhanced redundancy payments as long as they are kept in proportion to the statutory age bandings (see previous question for details of the statutory scheme and age bandings). So you could choose to remove the cap on a week’s pay across the board (or set a higher cap); apply a different multiplier to the age bandings as long as you keep the same age bandings and ensure the multipliers keep the same ratio as the statutory ones (e.g. 1 times, 2 times, 3 times; instead of the statutory ½ times, 1 times, 1½ times); or apply a multiplier to the total payment (e.g. 1.5 times statutory redundancy pay).
If you have an enhanced redundancy scheme that does not comply with the rules set under the Regulations, it makes it possible for younger employees to bring age discrimination claims on the basis that longer serving employees will have a larger redundancy payment than shorter serving employees, who would tend to be younger. The fact that what you are giving them is better than the statutory scheme would be of little significance. Without the protection afforded by the Act in respect of enhanced redundancy payments, you would have to rely on the argument that your scheme is a reasonable means of fulfilling a business need (e.g. encouraging loyalty or rewarding experience). As this legislation is still relatively new, this sort of argument is untested and it is difficult to say how successful it would be.
In short, it would be best to alter your scheme so that it complied with the allowable schemes set out in the Equality Act. However, if your scheme is contractual you would need to take advice on how to change it without running into breach of contract claims.