I have been told today that they are outsourcing the reception

If your employer is outsourcing your job and a new employer is taking over your employment then you would be expected to transfer over to them. Your existing terms and conditions should remain the same and the new employer will simply be stepping into the shoes of the existing one, allowing you to continue doing your job as it was done now. There may be slight changes made to it but in general all contractual terms would need to be retained. There are a few exceptions when contractual changes could be introduced too but this can only happen if they are needed for technical, organisational or economic (ETO) reasons.

If you do not wish to transfer then you have the option of opting out of the transfer but that would be classified as resigning.

The circumstances when you could potentially claim constructive dismissal is if the new employer is going to introduce significant changes to your existing contract where they cannot justify them for being for an ETO reason. In your case the reason you are trying to rely on is that your reception desk will be moving to a different area of the building. Unless your current contract specifically mentions where your desk is going to be then this would not be a contractual change and in general such a move would not be considered a significant change to your contract anyway. They are not altering your duties, reducing your pay, taking away benefits and so on. The new area may not be as nice as the old one but it is still a working station and as long as your other main terms are remaining the same then it is quite unlikely that this reason on its own can be used to justify a claim for constructive dismissal.

Hope this clarifies your position? If you could please let me know that would be great, thank you

Glad to have been of help, all the best