Before you pick up the pup seriously consider if you can afford it. Dogs are expensive to care for properly.
If you can't afford the vets fees your choice will be leaving the animal untreated, debt or PTS. What would you do with a £1000+ vet bill?
Our 6 years old labrador costs us:
£54/month in insurance (and that isn't top of the range, has a £4k limit which we have been close to twice and £85 excess. He has also been in the vets twice in the first couple of years with gastro problems which cost £400-£500 at time. When he had knee surgery for luxating patella dh and I had to take weeks of annual leave at different times to be at home for the dog)
£11/month for preventative flea, tick and worming treatments, annual health check and vaccination boosters. They should be proper prescription flea and worming treatment from the vets. Supermarket worming tablets don't cover lungworm which can be fatal. Supermarket flea treatments aren't effective.
£40/month in a reasonable quality kibble (you can obviously buy cheap crap food, but that wont meet all your dogs needs)
£80/month for 2 days dog walking service when dh and I are both out house for 5-6 hours.
That doesn't include all the other expenses which are not insignificant such as wet/cold weather shoes/boots and clothing for 1+ hour walks in the rain through muddy fields the winter, treats, beds, etc etc.
When they are a pup you will also need to pay for initial vaccinations, neutering. Training classes every week. Different harnesses, training leads etc as they grow. Cleaning products during housetraining. For us it included replacing a sofa, carpet, shoes, kitchen cabinet door he chewed during the night when he was a teething 1 year old! etc etc.
Of course you will love and care for your pup, but seriously think it through, this is a 10-15 year significant commitment you will be signing up for! Have you looked into the breed you are getting and looked at its likely health issues? I have a friend with a westie who did not have lifetime insurance cover and pays a small fortune every month for skin treatments which is very common with that breed.