Pollinator confusion

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Short answer:
I don't think you'll have a problem with pollination with what you're suggesting.
Plant any apple you like, or a Conference pear and you should get adequate crops once the tree is mature.


Long answer:

The nearby crab apples should be fine for pollinating any apple tree. Crabs usually produce a lot of good pollen and have long been favoured as pollinators by many commercial growers.

Conference pear is self-fertile, although self-pollinated fruits tend to be bent, smaller and lower quality than the fruits which are pollinated by a different pear variety.
Self-pollinated (inbred) fruits of any kind tend to be less good than those produced by pollination from a different variety.
Poor pollination in bad spring weather also reduces fruit quality.
Fruit quality is often related to the number and vigour of the pips within the fruit - and poorly-pollinated fruit with few or sickly/inbred pips often drops prematurely as the tree seeks to retain the best-seeded fruits and put the most energy into the strongest pips for the next generation.

Make sure you choose a rootstock that will give you the required size of tree and which is suitable for your conditions (I have no idea where Redditch happens to be).
As it's on a veg plot, you may have size limits - and neighbouring plots at risk of shade.
So don't go for a rootstock that's stronger than MM106 (apple), Quince A (pear) or St.Julien A (plum) unless your soil is poor.
You may want to consider M9, M26 (apple), Quince C (pear) or Pixy (plum) rootstock if the soil is quite good and if you want to keep them as bushes rather than trees.

It's worth noting that in areas with plentiful rainfall Conference pears can be damaged by scab; a fungal disease which causes black spots on the fruit and in bad attacks the spots merge and cause the fruit to split.
But I haven't encountered any other pears which are reliably self-fertile, easily available and resistant to scab. The few that are will have to be ordered from specialist mail-order nurseries.
Conference can also be prone to canker in wet weather - a disease which attacks the bark and often kills twigs, then if not removed promptly it spreads to numerous other twigs, kills whole branches and eventually the whole tree.

Common varieties of apples and pears - those found in the shops - tend to have poor resistance to pests and diseases (and sometimes special soil needs to grow well, being designed for commercial growers and not backyard growers whose unsprayed/unfed trees need to be more robust), while some of the shop varieties are "foreign" varieties that don't always ripen properly in the cool, damp UK climate.
On the subject of canker and russet apples: Egremont Russet used to have good canker resistance but I lost one a couple of years ago to canker, so it now looks like new strains of canker have emerged which can bypass ER's resistance. Its scab resistance also now seems to be teetering on the brink of failure in some areas.
But since being grown commercially seems to be a kiss of death for a variety's disease resistance (because the tens of thousands of commercial trees of that variety give the diseases plenty of chances to try to get past the disease resistance). Egremont Russet is now quite a popular russet choice for commercial growers, so its loss of disease resistance is to be expected.

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