Many thanks for your patience. I would not suggest that you go down the constructive dismissal route as that can be quite difficult to prove and win. Instead you may wish to consider unfair dismissal where you are arguing that the redundancy procedure was not fair because there is effectively two of you doing the same job, yet you are the only one being considered for redundancy. Ideally what should happen is that you are both placed head to head in the redundancy exercise and some fair selection method is adopted to decide which one of you stays and which one is made redundant.
However, instead of making claims it is of course preferential if you were to try and negotiate something with the employer, for example leaving under a settlement agreement. Whatever you would be happy to leave with, it also has to be something which the employer is happy to pay you. So whilst you do have grounds to negotiate with them and push for more than the minimum you are entitled to, you cannot force them to agree to it.
If the direct negotiations fail and they proceed with the redundancy, then your first step would be to appeal to them. If that also fails you must then consider engaging ACAS to start the early conciliation process. This is a free procedure which uses them as a negotiator to try and agree some kind of settlement with the employer. If that also fails then you have the last option of a tribunal claim. As mentioned there is a potential case for unfair dismissal if the employer did not follow a fair selection procedure and it would be for the employer to convince the tribunal that they had done everything by the book.
But try the direct negotiations first, propose to leave under a settlement agreement and do not hesitate to challenge them over what they are doing and even mention that you will be considering unfair dismissal if needed. So there are plenty of opportunities for negotiating and this could happen up until the very end, on the day of a tribunal hearing. The closer you get to that the more likely it is that the employer may be seeking a settlement rather than incur further legal costs and spend time and resources defending this.
I hope this has answered your query. I would be grateful if you could please take a second to leave a positive rating (3, 4 or 5 stars) as that is an important part of our process and recognises the time I have spent assisting you. If you need me to clarify anything before you go - please get back to me on here and I will assist further as best as I can. Thank you