One for the apple experts.

A few thoughts come to mind:

1.
It is a shoot from the rootstock - some rootstocks are crab apples.

2.
Someone has grafted a piece of crab apple to the main tree, to ensure good pollination. Alternatively, perhaps the tree was once a "family tree" grafted with up to four different varieties.
If you removed that branch, you might find that your main tree starts to crop less heavily or less regularly.

3.
It could be aphid damage, which can cause small, stunted twigs and fruits.

4.
It could be powdery mildew damage, which can cause stunted branches.

5.
It might be a mutation. Very occasionally a tree produces a mutant branch with somewhat different characteristics to the main tree.

.............

Thanks for the prompt reply FB as far as i know this is the first time this has happened. It does not seemed to have affected the rest of the tree so i will tell him its a mutation and we will keep an eye on it.One other question every year something is attacking the ripening fruit. There are signs of something boreing into the apple and a maggot can be found inside Any ideas and is there a sprey for this problem. Regards Mick,

Even if the branch is a mutation, it will not affect the rest of the tree, unless it grows so quickly that it crowds-out all the other branches.
It might just be a vigorous shoot which has been stopped by aphids and mildew before maturing.

Regarding the maggoty apples: it's probably codling moth larva. They tunnel into the fruits and hollow-out the core, filling it with sawdust-like excrement which they sometimes push out of the hole in the apple.
Maggot-damaged apples are likely to be the most colourful, the first to ripen and the first to drop onto the ground.
It is possible to carefully cut around the maggoty core and salvage quite a bit of the flesh.

Most people would either tolerate it, or will use sticky "pheromone" traps which attract the moths. Some people have made home-made traps from an old plastic milk bottle with a few half-inch holes in the sides - and containing the following ingredients, hung in the tree:

Water (for them to drown in)
Cider, apple juice or crushed apple (to attract them to the scent of apple)
Sugar or syrup (to attract them to the sweetness)

Rather like a wasp trap in a jam jar, but it must contain some apple to attract the adult moths.

Oh...forgot to mention.....

There are chemical sprays available, but you risk killing beneficial insects such as bees (which still visit the dried-up flowers weeks after blossom time).

Some apple varieties are much more prone to attack than others. Eaters which ripen in July, August and early September are most likely to be attacked, especially if they are strongly coloured, scented, thin-skinned, sweet and tasty (the maggots are as fussy as we are!).
Late-ripening apples and cooking apples tend to be much less affected.

But if they only have one tree to choose from, they've got no choice and even fairly maggot-resistant varieties can suffer heavy damage where no other trees are nearby to attract their attention.

The second picture looks quite like a crab apple...