Hello Michael.
Some confusion still exists about your licence and the vehicles you have. I will assume that you passed your test in April 2003, (after the 1997 licence changes)
I have been unable to find any data from my usual sources about the Abbey executive 430 models so I cannot confirm the information you have supplied. But your posting has rung a warning bell to me. Generally Abbey have used a model numbering system that increases along with size and weight of the caravan. And 430 falls amongst the larger numbers Abbey use.. Abbey vans with model numbers in the 400's have MIRO's between 893Kg and 1440Kg Consequently I am not convinced that your caravan only weighs 753Kg MIRO. I feel it is likely to be somewhat heavier.
Equally my sources do not list the 1998 Vectra Sri, but within the range the 1.8L saloons have do have a maximum permitted towed mass of 1400Kg with a kerb weight of 1300Kg or a little over depending on the model variations.
As I do not have verifiable data on either part of your combination I cannot offer definitive advice however I am concerned that your outfit may actually be illegal. You must seek clarification on the models you have and their respective weights. Do not rely on third party web sites, as my own investigations have demonstrated, either they are incomplete or do not cover every model made, or the information may be inaccurate. Check your data with the relevant hand books or data plates for the vehicles, or with the registered dealer or direct with the manufacturer.
The Law in this area is easily confused, so I urge you read the information available on the NTTA web site:
http://www.ntta.co.uk/law/
and if necessary confirm it with the DVLA or the Department for transport.
Please note that you with your post 1997 licence cannot tow a trailer where its maximum authorised mass (MAM) is greater than the kerbweight of the car - even if the trailer is not fully loaded and is actually less than the Kerbweight of the car. This is a point that Del did not make clear.