Clambers onto soap box.
Loose lead walking is much more than teaching your dog to walk well on a lead out and about.
So concentrate on reinforcing proximity to you whether you are, when in the house, in the garden etc.
Reward all eye contact every single time during the day. You will need to have treats on you all the time for a bit.
Initially reward eye contact when stationary and then after a few days add in eye contact when moving. Start this at home and reinforce and reinforce. It truly is like magic and you see your dog looking at you over and over again (almost so much that you get fed up with rewarding - keep rewarding you are doing really well!)
Reward your dog off lead when they are close to you, when they are in the heel postion, again do this at home to start with, and make sure you are consistent.
I would also get a harness with a front D ring and one on the back.
My wcs know that when the harness is on the back d ring they can walk ahead ( not pull but I am not expecting formal heelwork position) However when the d ring is on the front of the harness then they are walking in position.
By using the different positions on your harness you can have parts of your walk for "training heel work" and parts of your walk to just get from a to b without messing up your training.
Personally I hate the stop and start walking. It tends to frustrate both dog and the owner and actually increase the pulling.
Put in the time and loads of effort to eye focus and you will soon realise that you have a dog that does check in on you and hence less pulling. It is hard to pull if they are looking at you.
You will get a fab looking at you at home to start with and then go outside and it will all go to pot. Just stand still and wait for that eye contact, no command, no interaction just wait , the second you get it reward and can then move.
Walking in zig zags or drunk walking when you do not walk in one direction for more than 5 steps is less frustrating for your dog (than stop start walking) and also gives you more times to reinforce the correct behaviour.
Spaniels do like to walk with their noses down so also reward for any head of the ground motion.