Heat oven to 160C/fan 140C/gas 3. Grease a deep, medium-sized loaf tin (about 20 x 10cm, measured from the top), then line the base with a rectangle of non-stick baking paper.
Put the marmalade into a small pan, heat gently until melted (or use a microwaveproof jug or bowl, then cook on High for 30 secs). Beat in the lactose free yogurt, then let cool for a few mins.
Put the remaining cake ingredients into a large bowl and beat with an electric hand whisk until smooth. Quickly beat in the lactose free yogurt and marmalade mix, then pour into the prepared tin.
It will be quite runny. Leave the mix mounded in the middle of the tin rather than levelling the top, to help it rise and crack in the middle.
Bake for 1 hr-1 hr 10 mins until golden and well-risen; a skewer should come out clean. Take a look at the cake after 45 mins; if it has taken on a lot of colour, loosely cover with baking paper.
Meanwhile, heat the orange juice and marmalade in a small pan over a gentle heat until the marmalade melts (or use the microwave as before).
Set aside to cool, stirring now and again, until you have a thick, but still runny, glaze. When the cake is ready, cool in the tin for 10 mins, then turn onto a rack.
Spoon the topping over the cake while it’s just warm. The cake is best served the day it’s made, but will keep for up to 3 days tightly wrapped in an airtight container. Will freeze for up to 1 month, un-glazed.