Your right to an enhanced redundancy payment is now governed by the terms and conditions of your current employer, not the MOD. The number of years service that you have in calculating any such payment is the sum of the service with your current employer plus your MOD service (with the proviso that your service with both organisations was continuous - e.g. without a break in service).
When the MOD TUPE'd you across, considerable consultation will have taken place regarding existing contractual rights that you may have had as part of your MOD service, to cover the future possibility of redundancy. Unless your current employer has renegotiated those rights with you individually or collectively (if collective bargaining exists with your current employer), I would expect those rights to still stand FOR THE LENGTH OF YOUR MOD SERVICE ONLY. What does NOT necessarily transfer in 1997 was your right to future calculation of enhanced redundancy payments using the same formula as MOD was using in 1997 - unless it formed part of a deal that was struck with the new employer / MOD / PCS Union back in 1997.
In summary, what I am suggesting is that your entitlement to redundancy payments under enhanced terms (above the statutory minimum) is probably in two parts - one for your service up to 1997 and another since then. You can bet that the multiplier rates used will be less for your service since 1997 then that before.
Only your current employer can answer this question because it is tied to your current terms.